diff --git a/.rubocop.yml b/.rubocop.yml
index dbd74993..c92b709f 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -67,3 +67,5 @@ Style/MultilineBlockChain:
   Enabled: false
 Style/SpecialGlobalVars:
   Enabled: false
+Style/FrozenStringLiteralComment:
+  Enabled: false
diff --git a/.travis.yml b/.travis.yml
index e6bc197b..ac5a7f06 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,8 +7,6 @@ rvm:
   - ruby-head
   - 2.3.1
   - 2.2.4
-  - 2.1
-  - 2.0
 os:
   - linux
   # - osx
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7e4e2f4b..148aa2e2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,14 +1,41 @@
 master
 ===
 
-# 4.2.0
+# 4.1.13
 
-* Remove Rack support in favor of `resource.filters << proc { |oldbody| newbody }`
-* Expose `development?` and `production?` helpers to template context.
+* Change how config options are passed to Thor. Removes new Thor warnings from #2017
+
+# 4.1.12
+
+* Fix broken `ignore { |p| true }` form.
+
+# 4.1.11
+
+* Upgrade to Rack 2.
+
+# 4.1.10
+
+* Fix unicode issues in URL deeplinks.
+* Add prefix option to asset_hash (#1949)
+
+# 4.1.9
+
+* Fix `--watcher-*` CLI flags.
+* Allow spaces in paths to work with `link_to`. Fixes #1914
+* Add support for dotenv
+* Fix asset_url with asset_hash (#1919)
+* Allow partial lookups without a current_resource (#1912)
 
 # 4.1.8
 
+* Expose `development?` and `production?` helpers to template context.
+* require the `try` core extension (#1911)
+* Fix contract for Sitemap::Store.register_resource_list_manipulator (#1907)
+* Loosen contract on Resource#source_file to Maybe[String] (#1906)
 * Let collection loops access ConfigContext for helpers. #1879
+* Use https:// to clone templates (#1901)
+* Allow numbers to be unique page_ids (#1886)
+* Prevent infinite loop when encountering files where base filename is a possible templating engine
 
 # 4.1.7
 
diff --git a/Gemfile b/Gemfile
index f14eb3b1..db4043a0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -9,6 +9,12 @@ gem 'byebug'
 gem 'aruba', '~> 0.7.4', require: false
 gem 'rspec', '~> 3.0', require: false
 gem 'cucumber', '~> 2.0', require: false
+gem 'addressable', '~> 2.4.0', require: false
+
+# Pry tools
+gem 'pry'
+gem 'pry-stack_explorer'
+gem 'pry-rescue'
 
 # Optional middleman dependencies, included for tests
 gem 'haml', '>= 4.0.5', require: false
@@ -18,7 +24,7 @@ gem 'kramdown', '~> 1.2', require: false
 gem 'slim', '>= 2.0', require: false
 gem 'liquid', '>= 2.6', require: false
 gem 'stylus', '>= 1.0', require: false
-gem 'sinatra', '>= 1.4', require: false
+gem 'sinatra', '>= 2.0.0.beta2', require: false
 gem 'redcarpet', '>= 3.1', require: false
 
 # Dns server to test preview server
@@ -26,7 +32,7 @@ gem 'rubydns', '~> 1.0.1', require: false
 
 # To test javascript
 gem 'poltergeist', '~> 1.8', require: false
-gem 'phantomjs', '~> 1.9.8.0', require: false
+gem 'phantomjs', '~> 2.1.1.0', require: false
 
 # For less, note there is no compatible JS runtime for windows
 gem 'therubyrhino', '>= 2.0', platforms: :jruby
diff --git a/ISSUE_TEMPLATE.md b/ISSUE_TEMPLATE.md
new file mode 100644
index 00000000..6d2dc0e0
--- /dev/null
+++ b/ISSUE_TEMPLATE.md
@@ -0,0 +1,9 @@
+## Expected behavior and actual behavior
+
+## Steps to reproduce the problem (from a clean middleman installation)
+
+## Additional information
+
+- Ruby version: 
+- Middleman version: 
+- OS version: 
diff --git a/middleman-cli/bin/middleman b/middleman-cli/bin/middleman
index b5d1921d..8b381a08 100755
--- a/middleman-cli/bin/middleman
+++ b/middleman-cli/bin/middleman
@@ -9,6 +9,9 @@ end
 require "middleman-core/load_paths"
 Middleman.setup_load_paths
 
+require 'dotenv'
+::Dotenv.load
+
 require 'middleman-core'
 require 'middleman-core/logger'
 
@@ -22,12 +25,10 @@ module Middleman::Cli
       if setting.default.is_a?(String) || setting.default.is_a?(NilClass)
         base.class_option setting.key,
                           type: :string,
-                          default: :undefined,
                           desc: setting.description
       elsif setting.default.is_a?(TrueClass) || setting.default.is_a?(FalseClass)
         base.class_option setting.key,
                           type: :boolean,
-                          default: :undefined,
                           desc: setting.description
       end
     end
@@ -46,6 +47,8 @@ end
 
 ::Middleman::Logger.singleton(3)
 ::Middleman::Cli.config = ::Middleman::Application.new do
+  #
+  config[:environment] = (ENV['MM_ENV'] || ENV['RACK_ENV'] || 'development').to_sym
   config[:mode] = :config
   config[:exit_before_ready] = true
   config[:watcher_disable] = true
diff --git a/middleman-cli/lib/middleman-cli/build.rb b/middleman-cli/lib/middleman-cli/build.rb
index 7d5dd3af..9e521dde 100644
--- a/middleman-cli/lib/middleman-cli/build.rb
+++ b/middleman-cli/lib/middleman-cli/build.rb
@@ -10,7 +10,7 @@ module Middleman::Cli
 
     class_option :environment,
                  aliases: '-e',
-                 default: :production
+                 default: ENV['MM_ENV'] || ENV['RACK_ENV'] || :production
     class_option :clean,
                  type: :boolean,
                  default: true,
@@ -29,7 +29,7 @@ module Middleman::Cli
                  default: false,
                  desc: 'Print debug messages'
     class_option :instrument,
-                 type: :string,
+                 type: :boolean,
                  default: false,
                  desc: 'Print instrument messages'
     class_option :profile,
@@ -64,7 +64,7 @@ module Middleman::Cli
           config[:mode] = :build
           config[:show_exceptions] = false
           config[:cli_options] = cli_options.each_with_object({}) do |(k, v), sum|
-            sum[k] = v unless v == :undefined
+            sum[k] = v
           end
         end
 
diff --git a/middleman-cli/lib/middleman-cli/init.rb b/middleman-cli/lib/middleman-cli/init.rb
index f1c1927e..e8e5770c 100644
--- a/middleman-cli/lib/middleman-cli/init.rb
+++ b/middleman-cli/lib/middleman-cli/init.rb
@@ -113,7 +113,7 @@ module Middleman::Cli
     end
 
     def repository_path(repo)
-      repo.include?('://') || repo.include?('git@') ? repo : "git://github.com/#{repo}.git"
+      repo.include?('://') || repo.include?('git@') ? repo : "https://github.com/#{repo}.git"
     end
 
     # Add to CLI
diff --git a/middleman-cli/lib/middleman-cli/server.rb b/middleman-cli/lib/middleman-cli/server.rb
index 479f53bd..85e75a9f 100644
--- a/middleman-cli/lib/middleman-cli/server.rb
+++ b/middleman-cli/lib/middleman-cli/server.rb
@@ -17,7 +17,7 @@ module Middleman::Cli
                  default: false,
                  desc: 'Print debug messages'
     class_option :instrument,
-                 type: :string,
+                 type: :boolean,
                  default: false,
                  desc: 'Print instrument messages'
     class_option :profile,
diff --git a/middleman-cli/middleman-cli.gemspec b/middleman-cli/middleman-cli.gemspec
index f2719efc..e9447a9c 100644
--- a/middleman-cli/middleman-cli.gemspec
+++ b/middleman-cli/middleman-cli.gemspec
@@ -17,7 +17,7 @@ Gem::Specification.new do |s|
   s.test_files   = `git ls-files -z -- {fixtures,features}/*`.split("\0")
   s.executable   = 'middleman'
   s.require_path = 'lib'
-  s.required_ruby_version = '>= 2.0.0'
+  s.required_ruby_version = '>= 2.2.0'
 
   # CLI
   s.add_dependency('thor', ['>= 0.17.0', '< 2.0'])
diff --git a/middleman-core/features/asset_hash.feature b/middleman-core/features/asset_hash.feature
index 6b92777c..7c173800 100644
--- a/middleman-core/features/asset_hash.feature
+++ b/middleman-core/features/asset_hash.feature
@@ -188,6 +188,23 @@ Feature: Assets get file hashes appended to them and references to them are upda
     When I go to "/partials/"
     Then I should see 'href="../stylesheets/uses_partials-ec347271.css'
 
+  Scenario: The asset hash should change when a Rack-based filter changes
+    Given a fixture app "asset-hash-app"
+    And a file named "config.rb" with:
+      """
+      activate :asset_hash
+      activate :relative_assets
+      activate :directory_indexes
+      require 'lib/middleware.rb'
+      use ::Middleware
+      """
+    Given the Server is running at "asset-hash-app"
+    When I go to "/"
+    Then I should see 'href="stylesheets/site-5ad7def0.css'
+    When I go to "stylesheets/site-5ad7def0.css"
+    Then I should see 'background-image: url("../images/100px-5fd6fb90.jpg")'
+    Then I should see 'Added by Rack filter'
+
   Scenario: Hashed-asset files are not produced for ignored paths
     Given a fixture app "asset-hash-app"
     And a file named "config.rb" with:
@@ -291,3 +308,17 @@ Feature: Assets get file hashes appended to them and references to them are upda
       | javascripts/application.js.map |
 
     And the file "javascripts/application-4553338c.js" should contain "//# sourceMappingURL=application.js-22cc2b5f.map"
+
+  Scenario: Hashes can contain a prefix
+    Given a successfully built app at "asset-hash-prefix"
+    When I cd to "build"
+    Then the following files should exist:
+      | index.html |
+      | javascripts/application-myprefix-4553338c.js |
+      | javascripts/application.js-myprefix-22cc2b5f.map |
+      | index.html |
+    And the following files should not exist:
+      | javascripts/application.js |
+      | javascripts/application.js.map |
+
+    And the file "javascripts/application-myprefix-4553338c.js" should contain "//# sourceMappingURL=application.js-myprefix-22cc2b5f.map"
diff --git a/middleman-core/features/asset_host.feature b/middleman-core/features/asset_host.feature
index 646f1154..0433b61b 100644
--- a/middleman-core/features/asset_host.feature
+++ b/middleman-core/features/asset_host.feature
@@ -25,7 +25,8 @@ Feature: Alternate between multiple asset hosts
     And a file named "config.rb" with:
       """
       activate :asset_host, host: Proc.new { |asset|
-        "http://assets%d.example.com" % (asset.hash % 4)
+        hash = Digest::MD5.digest(asset).bytes.map!(&:ord).reduce(&:+)
+        "http://assets%d.example.com" % (hash % 4)
       }
       """
     And the Server is running
diff --git a/middleman-core/features/endpoints.feature b/middleman-core/features/endpoints.feature
deleted file mode 100644
index 1ff6aaf6..00000000
--- a/middleman-core/features/endpoints.feature
+++ /dev/null
@@ -1,17 +0,0 @@
-Feature: Generic block based pages
-
-  Scenario: Static Ruby Endpoints
-    Given an empty app
-    And a file named "config.rb" with:
-    """
-    endpoint "hello.html" do
-      "world"
-    end
-    """
-    And a file named "source/index.html.erb" with:
-    """
-    Hi
-    """
-    And the Server is running at "empty_app"
-    When I go to "/hello.html"
-    Then I should see "world"
diff --git a/middleman-core/features/extension_api_deprecations.feature b/middleman-core/features/extension_api_deprecations.feature
index 15f447ac..8c9dd216 100644
--- a/middleman-core/features/extension_api_deprecations.feature
+++ b/middleman-core/features/extension_api_deprecations.feature
@@ -3,9 +3,8 @@ Feature: Extension author could use some hooks
   Scenario: When build
     Given a fixture app "extension-api-deprecations-app"
     When I run `middleman build`
-    And the exit status should be 0
+    Then the exit status should be 0
     And the output should contain "`set :layout` is deprecated"
-    And the output should contain "Project built successfully"
     And the file "build/index.html" should contain "In Index"
     And the file "build/index.html" should not contain "In Layout"
 
diff --git a/middleman-core/features/extension_hooks.feature b/middleman-core/features/extension_hooks.feature
index 11a05557..1dedd9a9 100644
--- a/middleman-core/features/extension_hooks.feature
+++ b/middleman-core/features/extension_hooks.feature
@@ -7,6 +7,7 @@ Feature: Extension author could use some hooks
     And the output should contain "/// after_configuration ///"
     And the output should contain "/// ready ///"
     And the output should contain "/// before_build ///"
+    And the output should contain "/// before ///"
     And the output should contain "/// before_render ///"
     And the output should contain "/// after_render ///"
     And the output should contain "/// after_build ///"
diff --git a/middleman-core/features/helpers_link_to.feature b/middleman-core/features/helpers_link_to.feature
index 90b6f08a..fe8e8530 100644
--- a/middleman-core/features/helpers_link_to.feature
+++ b/middleman-core/features/helpers_link_to.feature
@@ -40,19 +40,29 @@ Feature: link_to helper
     """
     absolute: <%= link_to "Needs Index", "/needs_index.html", relative: true %>
     relative: <%= link_to "Relative", "needs_index.html", relative: true %>
+
+    absolute spaces: <%= link_to "Spaces Index", "/evil spaces.html", relative: true %>
+    relative spaces: <%= link_to "Spaces Relative", "evil spaces.html", relative: true %>
     """
     And a file named "source/link_to/sub.html.erb" with:
     """
     absolute: <%= link_to "Needs Index", "/needs_index.html", relative: true %>
     relative: <%= link_to "Relative", "../needs_index.html", relative: true %>
+
+    absolute spaces: <%= link_to "Spaces Index", "/evil spaces.html", relative: true %>
+    relative spaces: <%= link_to "Spaces Relative", "../evil spaces.html", relative: true %>
     """
     And the Server is running at "indexable-app"
     When I go to "/link_to.html"
     Then I should see 'absolute: <a href="needs_index.html">Needs Index</a>'
     Then I should see 'relative: <a href="needs_index.html">Relative</a>'
+    Then I should see 'absolute spaces: <a href="evil%20spaces.html">Spaces Index</a>'
+    Then I should see 'relative spaces: <a href="evil%20spaces.html">Spaces Relative</a>'
     When I go to "/link_to/sub.html"
     Then I should see 'absolute: <a href="../needs_index.html">Needs Index</a>'
     Then I should see 'relative: <a href="../needs_index.html">Relative</a>'
+    Then I should see 'absolute spaces: <a href="../evil%20spaces.html">Spaces Index</a>'
+    Then I should see 'relative spaces: <a href="../evil%20spaces.html">Spaces Relative</a>'
 
   Scenario: link_to relative works with strip_index_file
     Given a fixture app "indexable-app"
@@ -113,7 +123,7 @@ Feature: link_to helper
     When I go to "/link_to/sub.html"
     Then I should see 'absolute: <a href="../needs_index.html">Needs Index</a>'
     Then I should see 'relative: <a href="../needs_index.html">Relative</a>'
-  
+
   Scenario: link_to knows about directory indexes
     Given a fixture app "indexable-app"
     And a file named "source/link_to.html.erb" with:
diff --git a/middleman-core/features/i18n_link_to.feature b/middleman-core/features/i18n_link_to.feature
index a10787c4..9d3f0682 100644
--- a/middleman-core/features/i18n_link_to.feature
+++ b/middleman-core/features/i18n_link_to.feature
@@ -4,7 +4,7 @@ Feature: i18n Paths
     Given a fixture app "empty-app"
     And a file named "data/pages.yml" with:
       """
-      - hello.html 
+      - hello.html
       """
     And a file named "locales/en.yml" with:
       """
@@ -50,24 +50,24 @@ Feature: i18n Paths
     Given the Server is running at "empty-app"
     When I go to "/hello.html"
     Then I should see "Page: Hello"
-    Then I should see '<a class="current" href="/index.html">Current Home</a>'
-    Then I should see '<a title="Other Home" href="/es/index.html">Other Home</a>'
-    Then I should see '<a class="current" href="/index.html"><span>Home: Current Block</span></a>'
-    Then I should see '<a title="Other Home" href="/es/index.html"><span>Home: Other Block</span></a>'
-    Then I should see '<a class="current" href="/hello.html">Current hello.html</a>'
-    Then I should see '<a title="Other hello.html" href="/es/hola.html">Other hello.html</a>'
-    Then I should see '<a class="current" href="/hello.html"><span>Current Block</span></a>'
-    Then I should see '<a title="Other hello.html" href="/es/hola.html"><span>Other Block</span></a>'
+    Then I should see '<a href="/index.html" class="current">Current Home</a>'
+    Then I should see '<a href="/es/index.html" title="Other Home">Other Home</a>'
+    Then I should see '<a href="/index.html" class="current"><span>Home: Current Block</span></a>'
+    Then I should see '<a href="/es/index.html" title="Other Home"><span>Home: Other Block</span></a>'
+    Then I should see '<a href="/hello.html" class="current">Current hello.html</a>'
+    Then I should see '<a href="/es/hola.html" title="Other hello.html">Other hello.html</a>'
+    Then I should see '<a href="/hello.html" class="current"><span>Current Block</span></a>'
+    Then I should see '<a href="/es/hola.html" title="Other hello.html"><span>Other Block</span></a>'
     When I go to "/es/hola.html"
     Then I should see "Page: Hola"
-    Then I should see '<a class="current" href="/es/index.html">Current Home</a>'
-    Then I should see '<a title="Other Home" href="/index.html">Other Home</a>'
-    Then I should see '<a class="current" href="/es/index.html"><span>Home: Current Block</span></a>'
-    Then I should see '<a title="Other Home" href="/index.html"><span>Home: Other Block</span></a>'
-    Then I should see '<a class="current" href="/es/hola.html">Current hello.html</a>'
-    Then I should see '<a title="Other hello.html" href="/hello.html">Other hello.html</a>'
-    Then I should see '<a class="current" href="/es/hola.html"><span>Current Block</span></a>'
-    Then I should see '<a title="Other hello.html" href="/hello.html"><span>Other Block</span></a>'
+    Then I should see '<a href="/es/index.html" class="current">Current Home</a>'
+    Then I should see '<a href="/index.html" title="Other Home">Other Home</a>'
+    Then I should see '<a href="/es/index.html" class="current"><span>Home: Current Block</span></a>'
+    Then I should see '<a href="/index.html" title="Other Home"><span>Home: Other Block</span></a>'
+    Then I should see '<a href="/es/hola.html" class="current">Current hello.html</a>'
+    Then I should see '<a href="/hello.html" title="Other hello.html">Other hello.html</a>'
+    Then I should see '<a href="/es/hola.html" class="current"><span>Current Block</span></a>'
+    Then I should see '<a href="/hello.html" title="Other hello.html"><span>Other Block</span></a>'
 
   Scenario: link_to is i18n aware and supports relative_links
     Given a fixture app "empty-app"
@@ -124,30 +124,30 @@ Feature: i18n Paths
     Then I should see "assets/css/main.css"
     When I go to "/hello.html"
     Then I should see "Page: Hello"
-    Then I should see '<a class="current" href="index.html">Current Home</a>'
-    Then I should see '<a title="Other Home" href="es/index.html">Other Home</a>'
-    Then I should see '<a class="current" href="index.html"><span>Home: Current Block</span></a>'
-    Then I should see '<a title="Other Home" href="es/index.html"><span>Home: Other Block</span></a>'
-    Then I should see '<a class="current" href="hello.html">Current hello.html</a>'
-    Then I should see '<a title="Other hello.html" href="es/hola.html">Other hello.html</a>'
-    Then I should see '<a class="current" href="hello.html"><span>Current Block</span></a>'
-    Then I should see '<a title="Other hello.html" href="es/hola.html"><span>Other Block</span></a>'
+    Then I should see '<a href="index.html" class="current">Current Home</a>'
+    Then I should see '<a href="es/index.html" title="Other Home">Other Home</a>'
+    Then I should see '<a href="index.html" class="current"><span>Home: Current Block</span></a>'
+    Then I should see '<a href="es/index.html" title="Other Home"><span>Home: Other Block</span></a>'
+    Then I should see '<a href="hello.html" class="current">Current hello.html</a>'
+    Then I should see '<a href="es/hola.html" title="Other hello.html">Other hello.html</a>'
+    Then I should see '<a href="hello.html" class="current"><span>Current Block</span></a>'
+    Then I should see '<a href="es/hola.html" title="Other hello.html"><span>Other Block</span></a>'
     When I go to "/es/hola.html"
     Then I should see "Page: Hola"
-    Then I should see '<a class="current" href="index.html">Current Home</a>'
-    Then I should see '<a title="Other Home" href="../index.html">Other Home</a>'
-    Then I should see '<a class="current" href="index.html"><span>Home: Current Block</span></a>'
-    Then I should see '<a title="Other Home" href="../index.html"><span>Home: Other Block</span></a>'
-    Then I should see '<a class="current" href="hola.html">Current hello.html</a>'
-    Then I should see '<a title="Other hello.html" href="../hello.html">Other hello.html</a>'
-    Then I should see '<a class="current" href="hola.html"><span>Current Block</span></a>'
-    Then I should see '<a title="Other hello.html" href="../hello.html"><span>Other Block</span></a>'
+    Then I should see '<a href="index.html" class="current">Current Home</a>'
+    Then I should see '<a href="../index.html" title="Other Home">Other Home</a>'
+    Then I should see '<a href="index.html" class="current"><span>Home: Current Block</span></a>'
+    Then I should see '<a href="../index.html" title="Other Home"><span>Home: Other Block</span></a>'
+    Then I should see '<a href="hola.html" class="current">Current hello.html</a>'
+    Then I should see '<a href="../hello.html" title="Other hello.html">Other hello.html</a>'
+    Then I should see '<a href="hola.html" class="current"><span>Current Block</span></a>'
+    Then I should see '<a href="../hello.html" title="Other hello.html"><span>Other Block</span></a>'
 
   Scenario: url_for is i18n aware
     Given a fixture app "empty-app"
     And a file named "data/pages.yml" with:
       """
-      - hello.html 
+      - hello.html
       - article.html
       """
     And a file named "locales/en.yml" with:
diff --git a/middleman-core/features/markdown_redcarpet_in_slim.feature b/middleman-core/features/markdown_redcarpet_in_slim.feature
new file mode 100644
index 00000000..250c6857
--- /dev/null
+++ b/middleman-core/features/markdown_redcarpet_in_slim.feature
@@ -0,0 +1,41 @@
+Feature: Markdown support in Slim
+  In order to test support of the Slim markdown filter
+
+  Scenario: Markdown filter in Slim works
+    Given a fixture app "markdown-in-slim-app"
+    And a file named "config.rb" with:
+      """
+      set :markdown_engine, :redcarpet
+      activate :directory_indexes
+      """
+    And a file named "source/markdown_filter.html.slim" with:
+      """
+      markdown:
+        # H1
+
+        paragraph
+      """
+    Given the Server is running at "markdown-in-slim-app"
+    When I go to "/markdown_filter/"
+    Then I should see ">H1</h1>"
+    Then I should see "<p>paragraph</p>"
+
+
+  Scenario: Markdown filter in Slim uses our link_to and image_tag helpers
+    Given a fixture app "markdown-in-slim-app"
+    And a file named "config.rb" with:
+      """
+      set :markdown_engine, :redcarpet
+      activate :directory_indexes
+      """
+    And a file named "source/link_and_image.html.slim" with:
+      """
+      markdown:
+        [A link](/link_target.html)
+
+        ![image](blank.gif)
+      """
+    Given the Server is running at "markdown-in-slim-app"
+    When I go to "/link_and_image/"
+    Then I should see "/link_target/"
+    Then I should see 'src="/images/blank.gif"'
diff --git a/middleman-core/features/mount_rack.feature b/middleman-core/features/mount_rack.feature
new file mode 100644
index 00000000..dcb83146
--- /dev/null
+++ b/middleman-core/features/mount_rack.feature
@@ -0,0 +1,65 @@
+Feature: Support Rack apps mounted using map
+
+  Scenario: Mounted Rack App at /sinatra
+    Given the Server is running at "sinatra-app"
+    When I go to "/"
+    Then I should see "Hello World (Middleman)"
+    When I go to "/sinatra/"
+    Then I should see "Hello World (Sinatra)"
+
+  Scenario: Built Mounted Rack App at /sinatra
+    Given a successfully built app at "sinatra-app"
+    When I cd to "build"
+    Then the following files should exist:
+      | index.html |
+    Then the following files should not exist:
+      | sinatra/index.html |
+      | sinatra/index2.html |
+
+  Scenario: Static Ruby Endpoints
+    Given a fixture app "sinatra-app"
+    And a file named "config.rb" with:
+    """
+    endpoint "hello.html" do
+      "world"
+    end
+    """
+    And the Server is running at "sinatra-app"
+    When I go to "/hello.html"
+    Then I should see "world"
+
+  Scenario: Built Mounted Rack App at /sinatra (including rack endpoints)
+    Given a fixture app "sinatra-app"
+    And a file named "config.rb" with:
+      """
+      require "sinatra"
+
+      class MySinatra < Sinatra::Base
+        get "/" do
+          "Hello World (Sinatra)"
+        end
+        get "/derp.html" do
+          "De doo"
+        end
+      end
+
+      map "/sinatra" do
+        run MySinatra
+      end
+
+      endpoint "sinatra/index2.html", path: "/sinatra/"
+
+      endpoint "dedoo.html", path: "/sinatra/derp.html"
+
+      endpoint "hello.html" do
+        "world"
+      end
+      """
+    And a successfully built app at "sinatra-app"
+    When I cd to "build"
+    Then the following files should exist:
+      | index.html |
+      | sinatra/index2.html |
+      | dedoo.html |
+    And the file "sinatra/index2.html" should contain 'Hello World (Sinatra)'
+    And the file "dedoo.html" should contain 'De doo'
\ No newline at end of file
diff --git a/middleman-core/features/page-id.feature b/middleman-core/features/page-id.feature
index 63dd6fad..74d08cb5 100644
--- a/middleman-core/features/page-id.feature
+++ b/middleman-core/features/page-id.feature
@@ -3,14 +3,60 @@ Feature: Page IDs
   Scenario: link_to works with blocks (erb)
     Given the Server is running at "page-id-app"
     When I go to "/index.html"
-    Then I should see "I am: index.html"
+    Then I should see "I am: index"
     And I should see "URL1: /fm.html"
     And I should see "URL2: /2.html"
     And I should see 'URL3: <a href="/3.html">Hi</a>'
     And I should see 'URL4: <a href="/overwrites/from-default.html">Sym</a>'
+    And I should see 'URL5: <a href="/implicit.html">Imp</a>'
+    And I should see 'URL6: <a href="/folder/foldern.html">Foldern</a>'
+    And I should see 'URL7: <a href="/feed.xml">Feed</a>'
 
     When I go to "/fm.html"
     Then I should see "I am: frontmatter"
+    When I go to "/implicit.html"
+    Then I should see "I am: implicit"
+    When I go to "/feed.xml"
+    Then I should see "I am: feed.xml"
+    When I go to "/folder/foldern.html"
+    Then I should see "I am: folder/foldern"
+
+    When I go to "/1.html"
+    Then I should see "I am: page1"
+    When I go to "/2.html"
+    Then I should see "I am: page2"
+    When I go to "/3.html"
+    Then I should see "I am: page3"
+
+    When I go to "/overwrites/from-default.html"
+    Then I should see "I am: something-else"
+
+    When I go to "/overwrites/from-frontmatter.html"
+    Then I should see "I am: from_frontmatter"
+
+  Scenario: Override page ID derivation with a proc
+    Given a fixture app "page-id-app"
+    And app "page-id-app" is using config "proc"
+    And the Server is running at "page-id-app"
+
+    When I go to "/index.html"
+    Then I should see "I am: index.html-foo"
+    And I should see "URL1: /fm.html"
+    And I should see "URL2: /2.html"
+    And I should see 'URL3: <a href="/3.html">Hi</a>'
+    And I should see 'URL4: <a href="/overwrites/from-default.html">Sym</a>'
+    And I should see 'URL8: <a href="/implicit.html">Imp</a>'
+    And I should see 'URL9: <a href="/folder/foldern.html">Foldern</a>'
+    And I should see 'URL10: <a href="/feed.xml">Feed</a>'
+
+    When I go to "/fm.html"
+    Then I should see "I am: frontmatter"
+    When I go to "/implicit.html"
+    Then I should see "I am: implicit.html-foo"
+    When I go to "/feed.xml"
+    Then I should see "I am: feed.xml-foo"
+    When I go to "/folder/foldern.html"
+    Then I should see "I am: folder/foldern.html-foo"
 
     When I go to "/1.html"
     Then I should see "I am: page1"
diff --git a/middleman-core/features/relative_assets.feature b/middleman-core/features/relative_assets.feature
index ea6cbff0..ba131396 100644
--- a/middleman-core/features/relative_assets.feature
+++ b/middleman-core/features/relative_assets.feature
@@ -120,7 +120,7 @@ Feature: Relative Assets
       """
     And the Server is running at "relative-assets-app"
     When I go to "/sub/image_tag.html"
-    Then I should see '<img src="../img/blank.gif" />'
+    Then I should see '<img src="../img/blank.gif"'
 
   Scenario: Relative assets should not break data URIs in image_tag
     Given a fixture app "relative-assets-app"
diff --git a/middleman-core/features/relative_assets_helpers_only.feature b/middleman-core/features/relative_assets_helpers_only.feature
index 9d508977..194c8b37 100644
--- a/middleman-core/features/relative_assets_helpers_only.feature
+++ b/middleman-core/features/relative_assets_helpers_only.feature
@@ -72,7 +72,7 @@ Feature: Relative Assets (Helpers Only)
       """
     And the Server is running at "relative-assets-app"
     When I go to "/sub/image_tag.html"
-    Then I should see '<img src="../img/blank.gif" />'
+    Then I should see '<img src="../img/blank.gif"'
 
   Scenario: Relative assets should not break data URIs in image_tag
     Given a fixture app "relative-assets-app"
diff --git a/middleman-core/features/sass_in_slim.feature b/middleman-core/features/sass_in_slim.feature
new file mode 100644
index 00000000..d04055e4
--- /dev/null
+++ b/middleman-core/features/sass_in_slim.feature
@@ -0,0 +1,40 @@
+Feature: Sass/SCSS support in Slim
+  In order to test support of the Slim sass and scss filters
+
+  Scenario: Sass filter in Slim works
+    Given a fixture app "sass-in-slim-app"
+    And a file named "config.rb" with:
+      """
+      activate :directory_indexes
+      """
+    And a file named "source/sass_filter.html.slim" with:
+      """
+      sass:
+        .sass
+          margin: 0
+      """
+    Given the Server is running at "sass-in-slim-app"
+    When I go to "/sass_filter/"
+    Then I should see "text/css"
+    Then I should see ".sass"
+    Then I should see "margin:0"
+
+
+  Scenario: SCSS filter in Slim works
+    Given a fixture app "sass-in-slim-app"
+    And a file named "config.rb" with:
+      """
+      activate :directory_indexes
+      """
+    And a file named "source/scss_filter.html.slim" with:
+      """
+      scss:
+        .scss {
+          margin: 0;
+        }
+      """
+    Given the Server is running at "sass-in-slim-app"
+    When I go to "/scss_filter/"
+    Then I should see "text/css"
+    Then I should see ".scss"
+    Then I should see "margin:0"
diff --git a/middleman-core/fixtures/asset-hash-prefix/config.rb b/middleman-core/fixtures/asset-hash-prefix/config.rb
new file mode 100644
index 00000000..449a2e98
--- /dev/null
+++ b/middleman-core/fixtures/asset-hash-prefix/config.rb
@@ -0,0 +1,7 @@
+
+activate :asset_hash,
+  prefix: "myprefix-"
+
+activate :relative_assets
+
+activate :directory_indexes
diff --git a/middleman-core/fixtures/asset-hash-prefix/lib/middleware.rb b/middleman-core/fixtures/asset-hash-prefix/lib/middleware.rb
new file mode 100644
index 00000000..8ee825fd
--- /dev/null
+++ b/middleman-core/fixtures/asset-hash-prefix/lib/middleware.rb
@@ -0,0 +1,16 @@
+class Middleware
+  def initialize(app)
+    @app = app
+  end
+
+  def call(env)
+    status, headers, response = @app.call(env)
+    body = ''
+    response.each {|part| body += part }
+    if (env["PATH_INFO"] =~ /css$/)
+      body += "\n/* Added by Rack filter */"
+      status, headers, response = Rack::Response.new(body, status, headers).finish
+    end
+    [status, headers, response]
+  end
+end
diff --git a/middleman-core/fixtures/asset-hash-prefix/source/index.html.erb b/middleman-core/fixtures/asset-hash-prefix/source/index.html.erb
new file mode 100644
index 00000000..a88cc13f
--- /dev/null
+++ b/middleman-core/fixtures/asset-hash-prefix/source/index.html.erb
@@ -0,0 +1,6 @@
+<% content_for :head do %>
+  <title>The Middleman!</title>
+<% end %>
+
+<h1>Testing the sitemap hashing</h1>
+<br /><br /><br />
diff --git a/middleman-core/fixtures/asset-hash-prefix/source/javascripts/application.js b/middleman-core/fixtures/asset-hash-prefix/source/javascripts/application.js
new file mode 100644
index 00000000..c72f8572
--- /dev/null
+++ b/middleman-core/fixtures/asset-hash-prefix/source/javascripts/application.js
@@ -0,0 +1,2 @@
+function foo(){var message="HEY THERE FRIEND!";var para=document.createElement("p");para.innerHTML=message;var body=document.getElementsByTagName("body")[0];body.insertBefore(para,body.firstChild)}window.onload=foo;
+//# sourceMappingURL=application.js.map
diff --git a/middleman-core/fixtures/asset-hash-prefix/source/javascripts/application.js.map b/middleman-core/fixtures/asset-hash-prefix/source/javascripts/application.js.map
new file mode 100644
index 00000000..6a5acd5c
--- /dev/null
+++ b/middleman-core/fixtures/asset-hash-prefix/source/javascripts/application.js.map
@@ -0,0 +1 @@
+{"version":3,"sources":["source/javascripts/application.js"],"names":["foo","message","para","document","createElement","innerHTML","body","getElementsByTagName","insertBefore","firstChild","window","onload"],"mappings":"AAAA,QAASA,OACP,GAAIC,SAAU,mBACd,IAAIC,MAAOC,SAASC,cAAc,IAClCF,MAAKG,UAAYJ,OACb,IAAIK,MAAOH,SAASI,qBAAqB,QAAQ,EAC/CD,MAAKE,aAAaN,KAAMI,KAAKG,YAGpCC,OAAOC,OAASX"}
\ No newline at end of file
diff --git a/middleman-core/fixtures/asset-hash-prefix/source/layout.erb b/middleman-core/fixtures/asset-hash-prefix/source/layout.erb
new file mode 100644
index 00000000..c8aacecf
--- /dev/null
+++ b/middleman-core/fixtures/asset-hash-prefix/source/layout.erb
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+
+    <%= javascript_include_tag "application" %>
+    <%= yield_content :head %>
+  </head>
+
+  <body class="<%= page_classes %>">
+
+    <div id="main" role="main">
+      <%= yield %>
+    </div>
+
+  </body>
+</html>
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank12.gif b/middleman-core/fixtures/asset-host-app/source/images/blank12.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank41.gif b/middleman-core/fixtures/asset-host-app/source/images/blank41.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank42.gif b/middleman-core/fixtures/asset-host-app/source/images/blank42.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank5.gif b/middleman-core/fixtures/asset-host-app/source/images/blank5.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank51.gif b/middleman-core/fixtures/asset-host-app/source/images/blank51.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank52.gif b/middleman-core/fixtures/asset-host-app/source/images/blank52.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank6.gif b/middleman-core/fixtures/asset-host-app/source/images/blank6.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank61.gif b/middleman-core/fixtures/asset-host-app/source/images/blank61.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank62.gif b/middleman-core/fixtures/asset-host-app/source/images/blank62.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank7.gif b/middleman-core/fixtures/asset-host-app/source/images/blank7.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank71.gif b/middleman-core/fixtures/asset-host-app/source/images/blank71.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank72.gif b/middleman-core/fixtures/asset-host-app/source/images/blank72.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank8.gif b/middleman-core/fixtures/asset-host-app/source/images/blank8.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank81.gif b/middleman-core/fixtures/asset-host-app/source/images/blank81.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank82.gif b/middleman-core/fixtures/asset-host-app/source/images/blank82.gif
deleted file mode 100644
index e69de29b..00000000
diff --git a/middleman-core/fixtures/page-id-app/config-proc.rb b/middleman-core/fixtures/page-id-app/config-proc.rb
new file mode 100644
index 00000000..03070f0e
--- /dev/null
+++ b/middleman-core/fixtures/page-id-app/config-proc.rb
@@ -0,0 +1,7 @@
+%w(1 2 3).each do |n|
+  proxy "/#{n}.html", "/index.html", id: "page#{n}"
+end
+
+page "/overwrites/*", id: :"something-else"
+
+config[:page_id_generator] = ->(path){ path + "-foo" }
diff --git a/middleman-core/fixtures/page-id-app/source/feed.xml.erb b/middleman-core/fixtures/page-id-app/source/feed.xml.erb
new file mode 100644
index 00000000..a27800bd
--- /dev/null
+++ b/middleman-core/fixtures/page-id-app/source/feed.xml.erb
@@ -0,0 +1 @@
+I am: <%= current_resource.page_id %>
diff --git a/middleman-core/fixtures/page-id-app/source/folder/foldern.html.erb b/middleman-core/fixtures/page-id-app/source/folder/foldern.html.erb
new file mode 100644
index 00000000..a27800bd
--- /dev/null
+++ b/middleman-core/fixtures/page-id-app/source/folder/foldern.html.erb
@@ -0,0 +1 @@
+I am: <%= current_resource.page_id %>
diff --git a/middleman-core/fixtures/page-id-app/source/implicit.html.erb b/middleman-core/fixtures/page-id-app/source/implicit.html.erb
new file mode 100644
index 00000000..a27800bd
--- /dev/null
+++ b/middleman-core/fixtures/page-id-app/source/implicit.html.erb
@@ -0,0 +1 @@
+I am: <%= current_resource.page_id %>
diff --git a/middleman-core/fixtures/page-id-app/source/index.html.erb b/middleman-core/fixtures/page-id-app/source/index.html.erb
index 8f2997b6..6060bc3f 100644
--- a/middleman-core/fixtures/page-id-app/source/index.html.erb
+++ b/middleman-core/fixtures/page-id-app/source/index.html.erb
@@ -4,3 +4,11 @@ URL1: <%= url_for "frontmatter" %>
 URL2: <%= url_for "page2" %>
 URL3: <%= link_to "Hi", "page3" %>
 URL4: <%= link_to "Sym", :"something-else" %>
+URL5: <%= link_to "Imp", :implicit %>
+URL6: <%= link_to "Foldern", "folder/foldern" %>
+URL7: <%= link_to "Feed", "feed.xml" %>
+
+<%# If custom proc %>
+URL8: <%= link_to "Imp", "implicit.html-foo" %>
+URL9: <%= link_to "Foldern", "folder/foldern.html-foo" %>
+URL10: <%= link_to "Feed", "feed.xml-foo" %>
diff --git a/middleman-core/fixtures/asset-host-app/source/images/blank11.gif b/middleman-core/fixtures/sass-in-slim-app/config.rb
similarity index 100%
rename from middleman-core/fixtures/asset-host-app/source/images/blank11.gif
rename to middleman-core/fixtures/sass-in-slim-app/config.rb
diff --git a/middleman-core/fixtures/sinatra-app/config.rb b/middleman-core/fixtures/sinatra-app/config.rb
new file mode 100644
index 00000000..0251a715
--- /dev/null
+++ b/middleman-core/fixtures/sinatra-app/config.rb
@@ -0,0 +1,14 @@
+require "sinatra"
+
+class MySinatra < Sinatra::Base
+  get "/" do
+    "Hello World (Sinatra)"
+  end
+  get "/derp.html" do
+    "De doo"
+  end
+end
+
+map "/sinatra" do
+  run MySinatra
+end
diff --git a/middleman-core/fixtures/sinatra-app/source/index.html.erb b/middleman-core/fixtures/sinatra-app/source/index.html.erb
new file mode 100644
index 00000000..8b59c41c
--- /dev/null
+++ b/middleman-core/fixtures/sinatra-app/source/index.html.erb
@@ -0,0 +1,5 @@
+---
+layout: false
+---
+
+Hello World (Middleman)
\ No newline at end of file
diff --git a/middleman-core/lib/middleman-core/application.rb b/middleman-core/lib/middleman-core/application.rb
index 4ecd40f8..52b31c92 100644
--- a/middleman-core/lib/middleman-core/application.rb
+++ b/middleman-core/lib/middleman-core/application.rb
@@ -157,12 +157,12 @@ module Middleman
     define_setting :layout, :_auto_layout, 'Default layout name'
 
     # Which file extensions have a layout by default.
-    # @return [Set.<String>]
-    define_setting :extensions_with_layout, %w(.htm .html .xhtml .php), 'Which file extensions have a layout by default.', set: true
+    # @return [Array.<String>]
+    define_setting :extensions_with_layout, %w(.htm .html .xhtml .php), 'Which file extensions have a layout by default.'
 
     # Which file extensions are "assets."
     # @return [Array.<String>]
-    define_setting :asset_extensions, %w(.css .png .jpg .jpeg .webp .svg .svgz .js .gif .ttf .otf .woff .woff2 .eot .ico .map), 'Which file extensions are treated as assets.', set: true
+    define_setting :asset_extensions, %w(.css .png .jpg .jpeg .webp .svg .svgz .js .gif .ttf .otf .woff .woff2 .eot .ico .map), 'Which file extensions are treated as assets.'
 
     # Default string encoding for templates and output.
     # @return [String]
@@ -203,6 +203,7 @@ module Middleman
     define_setting :watcher_disable, false, 'If the Listen watcher should not run'
     define_setting :watcher_force_polling, false, 'If the Listen watcher should run in polling mode'
     define_setting :watcher_latency, nil, 'The Listen watcher latency'
+    define_setting :watcher_wait_for_delay, 0.5, 'The Listen watcher delay between calls when changes exist'
 
     # Delegate convenience methods off to their implementations
     def_delegator :"::Middleman::Logger", :singleton, :logger
@@ -266,6 +267,8 @@ module Middleman
       # Evaluate a passed block if given
       config_context.instance_exec(&block) if block_given?
 
+      apply_cli_options
+
       execute_callbacks(:before_sitemap)
 
       # Initialize the Sitemap
@@ -276,8 +279,6 @@ module Middleman
       # Before config is parsed, before extensions get to it.
       execute_callbacks(:initialized)
 
-      apply_cli_options
-
       # Before config is parsed. Mostly used for extensions.
       execute_callbacks(:before_configuration)
 
@@ -344,11 +345,11 @@ module Middleman
 
     # Clean up missing Tilt exts
     def prune_tilt_templates!
-      ::Tilt.mappings.each_key do |key|
+      ::Tilt.default_mapping.lazy_map.each_key do |key|
         begin
           ::Tilt[".#{key}"]
         rescue LoadError, NameError
-          ::Tilt.mappings.delete(key)
+          ::Tilt.default_mapping.lazy_map.delete(key)
         end
       end
     end
diff --git a/middleman-core/lib/middleman-core/builder.rb b/middleman-core/lib/middleman-core/builder.rb
index c84bfa39..1796d4d7 100644
--- a/middleman-core/lib/middleman-core/builder.rb
+++ b/middleman-core/lib/middleman-core/builder.rb
@@ -2,6 +2,7 @@ require 'pathname'
 require 'fileutils'
 require 'tempfile'
 require 'parallel'
+require 'middleman-core/rack'
 require 'middleman-core/callback_manager'
 require 'middleman-core/contracts'
 
@@ -38,6 +39,9 @@ module Middleman
       @cleaning = opts.fetch(:clean)
       @parallel = opts.fetch(:parallel, true)
 
+      rack_app = ::Middleman::Rack.new(@app).to_app
+      @rack = ::Rack::MockRequest.new(rack_app)
+
       @callbacks = ::Middleman::CallbackManager.new
       @callbacks.install_methods!(self, [:on_build_event])
     end
@@ -223,7 +227,15 @@ module Middleman
           if resource.binary?
             export_file!(output_file, resource.file_descriptor[:full_path])
           else
-            export_file!(output_file, binary_encode(resource.render))
+            response = @rack.get(::URI.escape(resource.request_path))
+
+            # If we get a response, save it to a tempfile.
+            if response.status == 200
+              export_file!(output_file, binary_encode(response.body))
+            else
+              trigger(:error, output_file, response.body)
+              return false
+            end
           end
         rescue => e
           trigger(:error, output_file, "#{e}\n#{e.backtrace.join("\n")}")
diff --git a/middleman-core/lib/middleman-core/configuration.rb b/middleman-core/lib/middleman-core/configuration.rb
index 0d6d9be7..c916fc90 100644
--- a/middleman-core/lib/middleman-core/configuration.rb
+++ b/middleman-core/lib/middleman-core/configuration.rb
@@ -1,5 +1,3 @@
-require 'set'
-
 module Middleman
   module Configuration
     # A class that manages a collection of documented settings.
@@ -131,37 +129,23 @@ module Middleman
 
       def initialize(key, default, description, options={})
         @value_set = false
-        @array_wrapped_value = nil
-        @array_wrapped_default = nil
         self.key = key
         self.default = default
         self.description = description
         self.options = options
-
-        @array_wrapped_default = if self.default && options[:set] && self.default.is_a?(Array)
-          Set.new(self.default)
-        end
       end
 
       # The user-supplied value for this setting, overriding the default
       def value=(value)
         @value = value
         @value_set = true
-
-        @array_wrapped_value = if @value && options[:set] && @value.is_a?(Array)
-          Set.new(@value)
-        end
       end
 
       # The effective value of the setting, which may be the default
       # if the user has not set a value themselves. Note that even if the
       # user sets the value to nil it will override the default.
       def value
-        if value_set?
-          @array_wrapped_value ? @array_wrapped_value : @value
-        else
-          @array_wrapped_default ? @array_wrapped_default : default
-        end
+        value_set? ? @value : default
       end
 
       # Whether or not there has been a value set beyond the default
diff --git a/middleman-core/lib/middleman-core/core_extensions.rb b/middleman-core/lib/middleman-core/core_extensions.rb
index ea31f89a..e38be937 100644
--- a/middleman-core/lib/middleman-core/core_extensions.rb
+++ b/middleman-core/lib/middleman-core/core_extensions.rb
@@ -19,6 +19,12 @@ Middleman::Extensions.register :data, auto_activate: :before_sitemap do
   Middleman::CoreExtensions::Data
 end
 
+# Rewrite embedded URLs via Rack
+Middleman::Extensions.register :inline_url_rewriter, auto_activate: :before_sitemap do
+  require 'middleman-core/core_extensions/inline_url_rewriter'
+  Middleman::CoreExtensions::InlineURLRewriter
+end
+
 # Catch and show exceptions at the Rack level
 Middleman::Extensions.register :show_exceptions, auto_activate: :before_configuration, modes: [:server] do
   require 'middleman-core/core_extensions/show_exceptions'
diff --git a/middleman-core/lib/middleman-core/core_extensions/file_watcher.rb b/middleman-core/lib/middleman-core/core_extensions/file_watcher.rb
index 82df8f73..6fd16ae9 100644
--- a/middleman-core/lib/middleman-core/core_extensions/file_watcher.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/file_watcher.rb
@@ -28,10 +28,7 @@ module Middleman
         super
 
         # Setup source collection.
-        @sources = ::Middleman::Sources.new(app,
-                                            disable_watcher: app.config[:watcher_disable],
-                                            force_polling: app.config[:watcher_force_polling],
-                                            latency: app.config[:watcher_latency])
+        @sources = ::Middleman::Sources.new(app)
 
         # Add default ignores.
         IGNORES.each do |key, value|
@@ -55,6 +52,13 @@ module Middleman
       # @return [void]
       Contract Any
       def after_configuration
+        @watcher.update_config(
+          disable_watcher: app.config[:watcher_disable],
+          force_polling: app.config[:watcher_force_polling],
+          latency: app.config[:watcher_latency],
+          wait_for_delay: app.config[:watcher_wait_for_delay]
+        )
+
         if @original_source_dir != app.config[:source]
           @watcher.update_path(app.config[:source])
         end
diff --git a/middleman-core/lib/middleman-core/core_extensions/inline_url_rewriter.rb b/middleman-core/lib/middleman-core/core_extensions/inline_url_rewriter.rb
new file mode 100644
index 00000000..43354e97
--- /dev/null
+++ b/middleman-core/lib/middleman-core/core_extensions/inline_url_rewriter.rb
@@ -0,0 +1,135 @@
+require 'rack'
+require 'rack/response'
+require 'memoist'
+require 'middleman-core/util'
+require 'middleman-core/contracts'
+
+module Middleman
+  module CoreExtensions
+    class InlineURLRewriter < ::Middleman::Extension
+      include Contracts
+
+      expose_to_application rewrite_inline_urls: :add
+
+      REWRITER_DESCRIPTOR = {
+        id: Symbol,
+        proc: Or[Proc, Method],
+        url_extensions: ArrayOf[String],
+        source_extensions: ArrayOf[String],
+        ignore: ArrayOf[::Middleman::Util::IGNORE_DESCRIPTOR],
+        after: Maybe[Symbol]
+      }.freeze
+
+      def initialize(app, options_hash={}, &block)
+        super
+
+        @rewriters = {}
+      end
+
+      Contract REWRITER_DESCRIPTOR => Any
+      def add(options)
+        @rewriters[options] = options
+      end
+
+      def after_configuration
+        return if @rewriters.empty?
+
+        rewriters = @rewriters.values.sort do |a, b|
+          if b[:after] && b[:after] == a[:id]
+            1
+          else
+            0
+          end
+        end
+
+        app.use Rack, rewriters: rewriters, middleman_app: @app
+      end
+
+      class Rack
+        extend Memoist
+        include Contracts
+
+        Contract RespondTo[:call], {
+          middleman_app: IsA['Middleman::Application'],
+          rewriters: ArrayOf[REWRITER_DESCRIPTOR]
+        } => Any
+        def initialize(app, options={})
+          @rack_app = app
+          @middleman_app = options.fetch(:middleman_app)
+          @rewriters = options.fetch(:rewriters)
+
+          all_source_exts = @rewriters
+                            .reduce([]) { |sum, rewriter| sum + rewriter[:source_extensions] }
+                            .flatten
+                            .uniq
+          @source_exts_regex_text = Regexp.union(all_source_exts).to_s
+
+          @all_asset_exts = @rewriters
+                            .reduce([]) { |sum, rewriter| sum + rewriter[:url_extensions] }
+                            .flatten
+                            .uniq
+        end
+
+        def call(env)
+          status, headers, response = @rack_app.call(env)
+
+          # Allow configuration or upstream request to skip all rewriting
+          return [status, headers, response] if env['bypass_inline_url_rewriter'] == 'true'
+
+          path = ::Middleman::Util.full_path(env['PATH_INFO'], @middleman_app)
+
+          return [status, headers, response] unless path =~ /(^\/$)|(#{@source_exts_regex_text}$)/
+          return [status, headers, response] unless body = ::Middleman::Util.extract_response_text(response)
+
+          dirpath = ::Pathname.new(File.dirname(path))
+
+          rewritten = ::Middleman::Util.instrument 'inline_url_rewriter', path: path do
+            ::Middleman::Util.rewrite_paths(body, path, @all_asset_exts, @middleman_app) do |asset_path|
+              uri = ::Middleman::Util.parse_uri(asset_path)
+
+              relative_path = uri.host.nil?
+
+              full_asset_path = if relative_path
+                dirpath.join(asset_path).to_s
+              else
+                asset_path
+              end
+
+              @rewriters.each do |rewriter|
+                uid = rewriter.fetch(:id)
+
+                # Allow upstream request to skip this specific rewriting
+                next if env["bypass_inline_url_rewriter_#{uid}"] == 'true'
+
+                exts = rewriter.fetch(:url_extensions)
+                next unless exts.include?(::File.extname(asset_path))
+
+                source_exts = rewriter.fetch(:source_extensions)
+                next unless source_exts.include?(::File.extname(path))
+
+                ignore = rewriter.fetch(:ignore)
+                next if ignore.any? { |r| ::Middleman::Util.should_ignore?(r, full_asset_path) }
+
+                rewrite_ignore = Array(rewriter[:rewrite_ignore] || [])
+                next if rewrite_ignore.any? { |i| ::Middleman::Util.path_match(i, path) }
+
+                proc = rewriter.fetch(:proc)
+
+                result = proc.call(asset_path, dirpath, path)
+                asset_path = result if result
+              end
+
+              asset_path
+            end
+          end
+
+          ::Rack::Response.new(
+            rewritten,
+            status,
+            headers
+          ).finish
+        end
+      end
+    end
+  end
+end
diff --git a/middleman-core/lib/middleman-core/extension.rb b/middleman-core/lib/middleman-core/extension.rb
index 0d1f212d..9805455a 100644
--- a/middleman-core/lib/middleman-core/extension.rb
+++ b/middleman-core/lib/middleman-core/extension.rb
@@ -60,7 +60,7 @@ module Middleman
   # There are also some less common hooks that can be listened to from within an extension's `initialize` method:
   #
   # * `app.before_render {|body, path, locs, template_class| ... }` - Manipulate template sources before they are rendered.
-  # * `app.after_render {|content, path, locs, template_class| ... }` - Manipulate output text after a template has been rendered.
+  # * `app.after_render {|content, path, locs, template_class| ... }` - Manipulate output text after a template has been rendered. It is also common to install a Rack middleware to do this instead.
   # * `app.ready { ... }` - Run code once Middleman is ready to serve or build files (after `after_configuration`).
 
   #
diff --git a/middleman-core/lib/middleman-core/extensions/asset_hash.rb b/middleman-core/lib/middleman-core/extensions/asset_hash.rb
index f78eed5e..3e2a02aa 100644
--- a/middleman-core/lib/middleman-core/extensions/asset_hash.rb
+++ b/middleman-core/lib/middleman-core/extensions/asset_hash.rb
@@ -1,15 +1,19 @@
 require 'middleman-core/util'
+require 'middleman-core/rack'
 
 class Middleman::Extensions::AssetHash < ::Middleman::Extension
-  option :sources, %w(.css .htm .html .js .php .xhtml), 'List of extensions that are searched for hashable assets.', set: true
-  option :exts, nil, 'List of extensions that get asset hashes appended to them.', set: true
+  option :sources, %w(.css .htm .html .js .php .xhtml), 'List of extensions that are searched for hashable assets.'
+  option :exts, nil, 'List of extensions that get asset hashes appended to them.'
   option :ignore, [], 'Regexes of filenames to skip adding asset hashes to'
   option :rewrite_ignore, [], 'Regexes of filenames to skip processing for path rewrites'
+  option :prefix, '', 'Prefix for hash'
 
   def initialize(app, options_hash={}, &block)
     super
 
+    require 'addressable/uri'
     require 'digest/sha1'
+    require 'rack/mock'
 
     # Allow specifying regexes to ignore, plus always ignore apple touch icons
     @ignore = Array(options.ignore) + [/^apple-touch-icon/]
@@ -17,6 +21,14 @@ class Middleman::Extensions::AssetHash < ::Middleman::Extension
     # Exclude .ico from the default list because browsers expect it
     # to be named "favicon.ico"
     @exts = options.exts || (app.config[:asset_extensions] - %w(.ico))
+
+    app.rewrite_inline_urls id: :asset_hash,
+                            url_extensions: @exts.sort.reverse,
+                            source_extensions: options.sources,
+                            ignore: @ignore,
+                            rewrite_ignore: options.rewrite_ignore,
+                            proc: method(:rewrite_url),
+                            after: :asset_host
   end
 
   Contract String, Or[String, Pathname], Any => Maybe[String]
@@ -34,6 +46,7 @@ class Middleman::Extensions::AssetHash < ::Middleman::Extension
 
     replacement_path = "/#{asset_page.destination_path}"
     replacement_path = Pathname.new(replacement_path).relative_path_from(dirpath).to_s if relative_path
+
     replacement_path
   end
 
@@ -41,18 +54,9 @@ class Middleman::Extensions::AssetHash < ::Middleman::Extension
   # @return Array<Middleman::Sitemap::Resource>
   Contract ResourceList => ResourceList
   def manipulate_resource_list(resources)
-    resources.each do |r|
-      next unless r.destination_path.end_with?('/', *options.sources)
-      next if Array(options.rewrite_ignore || []).any? do |i|
-        ::Middleman::Util.path_match(i, "/#{r.destination_path}")
-      end
-
-      r.filters << ::Middleman::InlineURLRewriter.new(:asset_hash,
-                                                      app,
-                                                      r,
-                                                      url_extensions: @exts,
-                                                      ignore: options.ignore,
-                                                      proc: method(:rewrite_url))
+    @rack_client ||= begin
+      rack_app = ::Middleman::Rack.new(app).to_app
+      ::Rack::MockRequest.new(rack_app)
     end
 
     # Process resources in order: binary images and fonts, then SVG, then JS/CSS.
@@ -78,12 +82,18 @@ class Middleman::Extensions::AssetHash < ::Middleman::Extension
     digest = if resource.binary?
       ::Digest::SHA1.file(resource.source_file).hexdigest[0..7]
     else
-      # Render without asset hash
-      body = resource.render { |f| !f.respond_to?(:filter_name) || f.filter_name != :asset_hash }
-      ::Digest::SHA1.hexdigest(body)[0..7]
+      # Render through the Rack interface so middleware and mounted apps get a shot
+      response = @rack_client.get(
+        ::URI.escape(resource.destination_path),
+        'bypass_inline_url_rewriter_asset_hash' => 'true'
+      )
+
+      raise "#{resource.path} should be in the sitemap!" unless response.status == 200
+
+      ::Digest::SHA1.hexdigest(response.body)[0..7]
     end
 
-    resource.destination_path = resource.destination_path.sub(/\.(\w+)$/) { |ext| "-#{digest}#{ext}" }
+    resource.destination_path = resource.destination_path.sub(/\.(\w+)$/) { |ext| "-#{options.prefix}#{digest}#{ext}" }
     resource
   end
 
diff --git a/middleman-core/lib/middleman-core/extensions/asset_host.rb b/middleman-core/lib/middleman-core/extensions/asset_host.rb
index b076299d..7cb83d07 100644
--- a/middleman-core/lib/middleman-core/extensions/asset_host.rb
+++ b/middleman-core/lib/middleman-core/extensions/asset_host.rb
@@ -1,3 +1,5 @@
+require 'addressable/uri'
+
 class Middleman::Extensions::AssetHost < ::Middleman::Extension
   option :host, nil, 'The asset host to use or a Proc to determine asset host', required: true
   option :exts, nil, 'List of extensions that get cache busters strings appended to them.'
@@ -5,22 +7,15 @@ class Middleman::Extensions::AssetHost < ::Middleman::Extension
   option :ignore, [], 'Regexes of filenames to skip adding query strings to'
   option :rewrite_ignore, [], 'Regexes of filenames to skip processing for host rewrites'
 
-  Contract ResourceList => ResourceList
-  def manipulate_resource_list(resources)
-    resources.each do |r|
-      next unless r.destination_path.end_with?('/', *options.sources)
-      next if Array(options.rewrite_ignore || []).any? do |i|
-        ::Middleman::Util.path_match(i, "/#{r.destination_path}")
-      end
+  def initialize(app, options_hash={}, &block)
+    super
 
-      r.filters << ::Middleman::InlineURLRewriter.new(:asset_host,
-                                                      app,
-                                                      r,
-                                                      after_filter: :asset_hash,
-                                                      url_extensions: options.exts || app.config[:asset_extensions],
-                                                      ignore: options.ignore,
-                                                      proc: method(:rewrite_url))
-    end
+    app.rewrite_inline_urls id: :asset_host,
+                            url_extensions: options.exts || app.config[:asset_extensions],
+                            source_extensions: options.sources,
+                            ignore: options.ignore,
+                            rewrite_ignore: options.rewrite_ignore,
+                            proc: method(:rewrite_url)
   end
 
   Contract String, Or[String, Pathname], Any => String
diff --git a/middleman-core/lib/middleman-core/extensions/cache_buster.rb b/middleman-core/lib/middleman-core/extensions/cache_buster.rb
index ea723a81..2de11632 100644
--- a/middleman-core/lib/middleman-core/extensions/cache_buster.rb
+++ b/middleman-core/lib/middleman-core/extensions/cache_buster.rb
@@ -1,25 +1,19 @@
 # The Cache Buster extension
 class Middleman::Extensions::CacheBuster < ::Middleman::Extension
-  option :exts, nil, 'List of extensions that get cache busters strings appended to them.', set: true
-  option :sources, %w(.css .htm .html .js .php .xhtml), 'List of extensions that are searched for bustable assets.', set: true
+  option :exts, nil, 'List of extensions that get cache busters strings appended to them.'
+  option :sources, %w(.css .htm .html .js .php .xhtml), 'List of extensions that are searched for bustable assets.'
   option :ignore, [], 'Regexes of filenames to skip adding query strings to'
   option :rewrite_ignore, [], 'Regexes of filenames to skip processing for path rewrites'
 
-  Contract ResourceList => ResourceList
-  def manipulate_resource_list(resources)
-    resources.each do |r|
-      next unless r.destination_path.end_with?('/', *options.sources)
-      next if Array(options.rewrite_ignore || []).any? do |i|
-        ::Middleman::Util.path_match(i, "/#{r.destination_path}")
-      end
+  def initialize(app, options_hash={}, &block)
+    super
 
-      r.filters << ::Middleman::InlineURLRewriter.new(:cache_buster,
-                                                      app,
-                                                      r,
-                                                      url_extensions: options.exts || app.config[:asset_extensions],
-                                                      ignore: options.ignore,
-                                                      proc: method(:rewrite_url))
-    end
+    app.rewrite_inline_urls id: :cache_buster,
+                            url_extensions: options.exts || app.config[:asset_extensions],
+                            source_extensions: options.sources,
+                            ignore: options.ignore,
+                            rewrite_ignore: options.rewrite_ignore,
+                            proc: method(:rewrite_url)
   end
 
   Contract String, Or[String, Pathname], Any => String
diff --git a/middleman-core/lib/middleman-core/extensions/directory_indexes.rb b/middleman-core/lib/middleman-core/extensions/directory_indexes.rb
index 3bc340ee..cef88868 100644
--- a/middleman-core/lib/middleman-core/extensions/directory_indexes.rb
+++ b/middleman-core/lib/middleman-core/extensions/directory_indexes.rb
@@ -1,5 +1,3 @@
-require 'set'
-
 # Directory Indexes extension
 class Middleman::Extensions::DirectoryIndexes < ::Middleman::Extension
   # This should run after most other sitemap manipulators so that it
@@ -13,7 +11,7 @@ class Middleman::Extensions::DirectoryIndexes < ::Middleman::Extension
     index_file = app.config[:index_file]
     new_index_path = "/#{index_file}"
 
-    extensions = Set.new(%w(.htm .html .php .xhtml))
+    extensions = %w(.htm .html .php .xhtml)
 
     resources.each do |resource|
       # Check if it would be pointless to reroute
diff --git a/middleman-core/lib/middleman-core/extensions/gzip.rb b/middleman-core/lib/middleman-core/extensions/gzip.rb
index a633f78f..0483fe32 100644
--- a/middleman-core/lib/middleman-core/extensions/gzip.rb
+++ b/middleman-core/lib/middleman-core/extensions/gzip.rb
@@ -10,7 +10,7 @@
 # to .css, .htm, .html, .js, and .xhtml
 #
 class Middleman::Extensions::Gzip < ::Middleman::Extension
-  option :exts, %w(.css .htm .html .js .svg .xhtml), 'File extensions to Gzip when building.', set: true
+  option :exts, %w(.css .htm .html .js .svg .xhtml), 'File extensions to Gzip when building.'
   option :ignore, [], 'Patterns to avoid gzipping'
   option :overwrite, false, 'Overwrite original files instead of adding .gz extension.'
 
diff --git a/middleman-core/lib/middleman-core/extensions/minify_css.rb b/middleman-core/lib/middleman-core/extensions/minify_css.rb
index 9174322f..aca9c60b 100644
--- a/middleman-core/lib/middleman-core/extensions/minify_css.rb
+++ b/middleman-core/lib/middleman-core/extensions/minify_css.rb
@@ -1,5 +1,6 @@
+require 'active_support/core_ext/object/try'
+require 'memoist'
 require 'middleman-core/contracts'
-require 'rack/mime'
 
 # Minify CSS Extension
 class Middleman::Extensions::MinifyCss < ::Middleman::Extension
@@ -9,10 +10,17 @@ class Middleman::Extensions::MinifyCss < ::Middleman::Extension
     require 'sass'
     SassCompressor
   }, 'Set the CSS compressor to use.'
-  option :content_types, %w(text/css), 'Content types of resources that contain CSS', set: true
-  option :inline_content_types, %w(text/html text/php), 'Content types of resources that contain inline CSS', set: true
+  option :content_types, %w(text/css), 'Content types of resources that contain CSS'
+  option :inline_content_types, %w(text/html text/php), 'Content types of resources that contain inline CSS'
 
-  INLINE_CSS_REGEX = /(<style[^>]*>\s*(?:\/\*<!\[CDATA\[\*\/\n)?)(.*?)((?:(?:\n\s*)?\/\*\]\]>\*\/)?\s*<\/style>)/m
+  def ready
+    # Setup Rack middleware to minify CSS
+    app.use Rack, compressor: options[:compressor],
+                  ignore: Array(options[:ignore]) + [/\.min\./],
+                  inline: options[:inline],
+                  content_types: options[:content_types],
+                  inline_content_types: options[:inline_content_types]
+  end
 
   class SassCompressor
     def self.compress(style, options={})
@@ -22,61 +30,97 @@ class Middleman::Extensions::MinifyCss < ::Middleman::Extension
     end
   end
 
-  def initialize(app, options_hash={}, &block)
-    super
+  # Rack middleware to look for CSS and compress it
+  class Rack
+    extend Memoist
+    include Contracts
+    INLINE_CSS_REGEX = /(<style[^>]*>\s*(?:\/\*<!\[CDATA\[\*\/\n)?)(.*?)((?:(?:\n\s*)?\/\*\]\]>\*\/)?\s*<\/style>)/m
 
-    @ignore = Array(options[:ignore]) + [/\.min\./]
-    @compressor = options[:compressor]
-    @compressor = @compressor.to_proc if @compressor.respond_to? :to_proc
-    @compressor = @compressor.call if @compressor.is_a? Proc
-  end
+    # Init
+    # @param [Class] app
+    # @param [Hash] options
+    Contract RespondTo[:call], {
+      ignore: ArrayOf[PATH_MATCHER],
+      inline: Bool,
+      compressor: Or[Proc, RespondTo[:to_proc], RespondTo[:compress]]
+    } => Any
+    def initialize(app, options={})
+      @app = app
+      @ignore = options.fetch(:ignore)
+      @inline = options.fetch(:inline)
 
-  Contract ResourceList => ResourceList
-  def manipulate_resource_list(resources)
-    resources.each do |r|
-      type = r.content_type.try(:slice, /^[^;]*/)
-      if options[:inline] && minifiable_inline?(type)
-        r.filters << method(:minify_inline)
-      elsif minifiable?(type) && !ignore?(r.destination_path)
-        r.filters << method(:minify)
+      @compressor = options.fetch(:compressor)
+      @compressor = @compressor.to_proc if @compressor.respond_to? :to_proc
+      @compressor = @compressor.call if @compressor.is_a? Proc
+      @content_types = options[:content_types]
+      @inline_content_types = options[:inline_content_types]
+    end
+
+    # Rack interface
+    # @param [Rack::Environmemt] env
+    # @return [Array]
+    def call(env)
+      status, headers, response = @app.call(env)
+
+      content_type = headers['Content-Type'].try(:slice, /^[^;]*/)
+      path = env['PATH_INFO']
+
+      minified = if @inline && minifiable_inline?(content_type)
+        minify_inline(::Middleman::Util.extract_response_text(response))
+      elsif minifiable?(content_type) && !ignore?(path)
+        minify(::Middleman::Util.extract_response_text(response))
+      end
+
+      if minified
+        headers['Content-Length'] = minified.bytesize.to_s
+        response = [minified]
+      end
+
+      [status, headers, response]
+    end
+
+    private
+
+    # Whether the path should be ignored
+    # @param [String] path
+    # @return [Boolean]
+    def ignore?(path)
+      @ignore.any? { |ignore| ::Middleman::Util.path_match(ignore, path) }
+    end
+    memoize :ignore?
+
+    # Whether this type of content can be minified
+    # @param [String, nil] content_type
+    # @return [Boolean]
+    def minifiable?(content_type)
+      @content_types.include?(content_type)
+    end
+    memoize :minifiable?
+
+    # Whether this type of content contains inline content that can be minified
+    # @param [String, nil] content_type
+    # @return [Boolean]
+    def minifiable_inline?(content_type)
+      @inline_content_types.include?(content_type)
+    end
+    memoize :minifiable_inline?
+
+    # Minify the content
+    # @param [String] content
+    # @return [String]
+    def minify(content)
+      @compressor.compress(content)
+    end
+    memoize :minify
+
+    # Detect and minify inline content
+    # @param [String] content
+    # @return [String]
+    def minify_inline(content)
+      content.gsub(INLINE_CSS_REGEX) do
+        $1 + minify($2) + $3
       end
     end
+    memoize :minify_inline
   end
-
-  # Whether the path should be ignored
-  Contract String => Bool
-  def ignore?(path)
-    @ignore.any? { |ignore| ::Middleman::Util.path_match(ignore, path) }
-  end
-  memoize :ignore?
-
-  # Whether this type of content can be minified
-  Contract Maybe[String] => Bool
-  def minifiable?(content_type)
-    options[:content_types].include?(content_type)
-  end
-  memoize :minifiable?
-
-  # Whether this type of content contains inline content that can be minified
-  Contract Maybe[String] => Bool
-  def minifiable_inline?(content_type)
-    options[:inline_content_types].include?(content_type)
-  end
-  memoize :minifiable_inline?
-
-  # Minify the content
-  Contract String => String
-  def minify(content)
-    @compressor.compress(content)
-  end
-  memoize :minify
-
-  # Detect and minify inline content
-  Contract String => String
-  def minify_inline(content)
-    content.gsub(INLINE_CSS_REGEX) do
-      $1 + minify($2) + $3
-    end
-  end
-  memoize :minify_inline
 end
diff --git a/middleman-core/lib/middleman-core/extensions/minify_javascript.rb b/middleman-core/lib/middleman-core/extensions/minify_javascript.rb
index 02172e91..714d0645 100644
--- a/middleman-core/lib/middleman-core/extensions/minify_javascript.rb
+++ b/middleman-core/lib/middleman-core/extensions/minify_javascript.rb
@@ -1,3 +1,4 @@
+require 'active_support/core_ext/object/try'
 require 'middleman-core/contracts'
 require 'memoist'
 
@@ -9,79 +10,122 @@ class Middleman::Extensions::MinifyJavascript < ::Middleman::Extension
     require 'uglifier'
     ::Uglifier.new
   }, 'Set the JS compressor to use.'
-  option :content_types, %w(application/javascript), 'Content types of resources that contain JS', set: true
-  option :inline_content_types, %w(text/html text/php), 'Content types of resources that contain inline JS', set: true
+  option :content_types, %w(application/javascript), 'Content types of resources that contain JS'
+  option :inline_content_types, %w(text/html text/php), 'Content types of resources that contain inline JS'
 
-  INLINE_JS_REGEX = /(<script[^>]*>\s*(?:\/\/(?:(?:<!--)|(?:<!\[CDATA\[))\n)?)(.*?)((?:(?:\n\s*)?\/\/(?:(?:-->)|(?:\]\]>)))?\s*<\/script>)/m
-
-  def initialize(app, options_hash={}, &block)
-    super
-
-    @ignore = Array(options[:ignore]) + [/\.min\./]
-    @compressor = options[:compressor]
-    @compressor = @compressor.to_proc if @compressor.respond_to? :to_proc
-    @compressor = @compressor.call if @compressor.is_a? Proc
+  def ready
+    # Setup Rack middleware to minify JS
+    app.use Rack, compressor: options[:compressor],
+                  ignore: Array(options[:ignore]) + [/\.min\./],
+                  inline: options[:inline],
+                  content_types: options[:content_types],
+                  inline_content_types: options[:inline_content_types]
   end
 
-  Contract ResourceList => ResourceList
-  def manipulate_resource_list(resources)
-    resources.each do |r|
-      type = r.content_type.try(:slice, /^[^;]*/)
-      if options[:inline] && minifiable_inline?(type)
-        r.filters << method(:minify_inline)
-      elsif minifiable?(type) && !ignore?(r.destination_path)
-        r.filters << method(:minify)
+  # Rack middleware to look for JS and compress it
+  class Rack
+    extend Memoist
+    include Contracts
+    INLINE_JS_REGEX = /(<script[^>]*>\s*(?:\/\/(?:(?:<!--)|(?:<!\[CDATA\[))\n)?)(.*?)((?:(?:\n\s*)?\/\/(?:(?:-->)|(?:\]\]>)))?\s*<\/script>)/m
+
+    # Init
+    # @param [Class] app
+    # @param [Hash] options
+    Contract RespondTo[:call], {
+      ignore: ArrayOf[PATH_MATCHER],
+      inline: Bool,
+      compressor: Or[Proc, RespondTo[:to_proc], RespondTo[:compress]]
+    } => Any
+    def initialize(app, options={})
+      @app = app
+      @ignore = options.fetch(:ignore)
+      @inline = options.fetch(:inline)
+
+      @compressor = options.fetch(:compressor)
+      @compressor = @compressor.to_proc if @compressor.respond_to? :to_proc
+      @compressor = @compressor.call if @compressor.is_a? Proc
+      @content_types = options[:content_types]
+      @inline_content_types = options[:inline_content_types]
+    end
+
+    # Rack interface
+    # @param [Rack::Environmemt] env
+    # @return [Array]
+    def call(env)
+      status, headers, response = @app.call(env)
+
+      type = headers['Content-Type'].try(:slice, /^[^;]*/)
+      @path = env['PATH_INFO']
+
+      minified = if @inline && minifiable_inline?(type)
+        minify_inline(::Middleman::Util.extract_response_text(response))
+      elsif minifiable?(type) && !ignore?(@path)
+        minify(::Middleman::Util.extract_response_text(response))
+      end
+
+      if minified
+        headers['Content-Length'] = minified.bytesize.to_s
+        response = [minified]
+      end
+
+      [status, headers, response]
+    end
+
+    private
+
+    # Whether the path should be ignored
+    # @param [String] path
+    # @return [Boolean]
+    def ignore?(path)
+      @ignore.any? { |ignore| Middleman::Util.path_match(ignore, path) }
+    end
+    memoize :ignore?
+
+    # Whether this type of content can be minified
+    # @param [String, nil] content_type
+    # @return [Boolean]
+    def minifiable?(content_type)
+      @content_types.include?(content_type)
+    end
+    memoize :minifiable?
+
+    # Whether this type of content contains inline content that can be minified
+    # @param [String, nil] content_type
+    # @return [Boolean]
+    def minifiable_inline?(content_type)
+      @inline_content_types.include?(content_type)
+    end
+    memoize :minifiable_inline?
+
+    # Minify the content
+    # @param [String] content
+    # @return [String]
+    def minify(content)
+      @compressor.compress(content)
+    rescue ExecJS::ProgramError => e
+      warn "WARNING: Couldn't compress JavaScript in #{@path}: #{e.message}"
+      content
+    end
+    memoize :minify
+
+    # Detect and minify inline content
+    # @param [String] content
+    # @return [String]
+    def minify_inline(content)
+      content.gsub(INLINE_JS_REGEX) do |match|
+        first = $1
+        inline_content = $2
+        last = $3
+
+        # Only compress script tags that contain JavaScript (as opposed to
+        # something like jQuery templates, identified with a "text/html" type).
+        if !first.include?('type=') || first.include?('text/javascript')
+          first + minify(inline_content) + last
+        else
+          match
+        end
       end
     end
+    memoize :minify_inline
   end
-
-  # Whether the path should be ignored
-  Contract String => Bool
-  def ignore?(path)
-    @ignore.any? { |ignore| ::Middleman::Util.path_match(ignore, path) }
-  end
-  memoize :ignore?
-
-  # Whether this type of content can be minified
-  Contract Maybe[String] => Bool
-  def minifiable?(content_type)
-    options[:content_types].include?(content_type)
-  end
-  memoize :minifiable?
-
-  # Whether this type of content contains inline content that can be minified
-  Contract Maybe[String] => Bool
-  def minifiable_inline?(content_type)
-    options[:inline_content_types].include?(content_type)
-  end
-  memoize :minifiable_inline?
-
-  # Minify the content
-  Contract String => String
-  def minify(content)
-    @compressor.compress(content)
-  rescue ::ExecJS::ProgramError => e
-    warn "WARNING: Couldn't compress JavaScript in #{@path}: #{e.message}"
-    content
-  end
-  memoize :minify
-
-  # Detect and minify inline content
-  Contract String => String
-  def minify_inline(content)
-    content.gsub(INLINE_JS_REGEX) do |match|
-      first = $1
-      inline_content = $2
-      last = $3
-
-      # Only compress script tags that contain JavaScript (as opposed to
-      # something like jQuery templates, identified with a "text/html" type).
-      if !first.include?('type=') || first.include?('text/javascript')
-        first + minify(inline_content) + last
-      else
-        match
-      end
-    end
-  end
-  memoize :minify_inline
 end
diff --git a/middleman-core/lib/middleman-core/extensions/relative_assets.rb b/middleman-core/lib/middleman-core/extensions/relative_assets.rb
index 4d2e15db..432072c3 100644
--- a/middleman-core/lib/middleman-core/extensions/relative_assets.rb
+++ b/middleman-core/lib/middleman-core/extensions/relative_assets.rb
@@ -1,28 +1,24 @@
+require 'addressable/uri'
+
 # Relative Assets extension
 class Middleman::Extensions::RelativeAssets < ::Middleman::Extension
-  option :exts, nil, 'List of extensions that get converted to relative paths.', set: true
-  option :sources, %w(.css .htm .html .xhtml), 'List of extensions that are searched for relative assets.', set: true
+  option :exts, nil, 'List of extensions that get converted to relative paths.'
+  option :sources, %w(.css .htm .html .xhtml), 'List of extensions that are searched for relative assets.'
   option :ignore, [], 'Regexes of filenames to skip converting to relative paths.'
   option :rewrite_ignore, [], 'Regexes of filenames to skip processing for path rewrites.'
   option :helpers_only, false, 'Allow only Ruby helpers to change paths.'
 
-  Contract ResourceList => ResourceList
-  def manipulate_resource_list(resources)
-    return resources if options[:helpers_only]
+  def initialize(app, options_hash={}, &block)
+    super
 
-    resources.each do |r|
-      next unless r.destination_path.end_with?('/', *options.sources)
-      next if Array(options.rewrite_ignore || []).any? do |i|
-        ::Middleman::Util.path_match(i, "/#{r.destination_path}")
-      end
+    return if options[:helpers_only]
 
-      r.filters << ::Middleman::InlineURLRewriter.new(:relative_assets,
-                                                      app,
-                                                      r,
-                                                      url_extensions: options.exts || app.config[:asset_extensions],
-                                                      ignore: options.ignore,
-                                                      proc: method(:rewrite_url))
-    end
+    app.rewrite_inline_urls id: :relative_assets,
+                            url_extensions: options.exts || app.config[:asset_extensions],
+                            source_extensions: options.sources,
+                            ignore: options.ignore,
+                            rewrite_ignore: options.rewrite_ignore,
+                            proc: method(:rewrite_url)
   end
 
   def mark_as_relative(file_path, opts, current_resource)
diff --git a/middleman-core/lib/middleman-core/file_renderer.rb b/middleman-core/lib/middleman-core/file_renderer.rb
index a3e8b193..26a38dc7 100644
--- a/middleman-core/lib/middleman-core/file_renderer.rb
+++ b/middleman-core/lib/middleman-core/file_renderer.rb
@@ -3,8 +3,8 @@ require 'active_support/core_ext/string/output_safety'
 require 'active_support/core_ext/module/delegation'
 require 'middleman-core/contracts'
 
-::Tilt.mappings.delete('html') # WTF, Tilt?
-::Tilt.mappings.delete('csv')
+::Tilt.default_mapping.lazy_map.delete('html')
+::Tilt.default_mapping.lazy_map.delete('csv')
 
 module Middleman
   class FileRenderer
@@ -123,8 +123,8 @@ module Middleman
         # Find all the engines which handle this extension in tilt. Look for
         # config variables of that name and merge it
         extension_class = ::Middleman::Util.tilt_class(ext)
-        ::Tilt.mappings.each do |mapping_ext, engines|
-          next unless engines.include? extension_class
+
+        ::Tilt.default_mapping.extensions_for(extension_class).each do |mapping_ext|
           engine_options = @app.config[mapping_ext.to_sym] || {}
           options.merge!(engine_options)
         end
diff --git a/middleman-core/lib/middleman-core/inline_url_rewriter.rb b/middleman-core/lib/middleman-core/inline_url_rewriter.rb
deleted file mode 100644
index ae572313..00000000
--- a/middleman-core/lib/middleman-core/inline_url_rewriter.rb
+++ /dev/null
@@ -1,49 +0,0 @@
-require 'middleman-core/util'
-require 'middleman-core/contracts'
-
-module Middleman
-  class InlineURLRewriter
-    include Contracts
-
-    attr_reader :filter_name
-    attr_reader :after_filter
-
-    def initialize(filter_name, app, resource, options={})
-      @filter_name = filter_name
-      @app = app
-      @resource = resource
-      @options = options
-
-      @after_filter = @options.fetch(:after_filter, nil)
-    end
-
-    Contract String => String
-    def execute_filter(body)
-      path = "/#{@resource.destination_path}"
-      dirpath = ::Pathname.new(File.dirname(path))
-
-      ::Middleman::Util.instrument 'inline_url_rewriter', path: path do
-        ::Middleman::Util.rewrite_paths(body, path, @options.fetch(:url_extensions), @app) do |asset_path|
-          uri = ::Middleman::Util.parse_uri(asset_path)
-
-          relative_path = uri.host.nil?
-          full_asset_path = if relative_path
-            dirpath.join(asset_path).to_s
-          else
-            asset_path
-          end
-
-          exts = @options.fetch(:url_extensions)
-          next unless exts.include?(::File.extname(asset_path))
-
-          next if @options.fetch(:ignore).any? { |r| ::Middleman::Util.should_ignore?(r, full_asset_path) }
-
-          result = @options.fetch(:proc).call(asset_path, dirpath, path)
-          asset_path = result if result
-
-          asset_path
-        end
-      end
-    end
-  end
-end
diff --git a/middleman-core/lib/middleman-core/preview_server.rb b/middleman-core/lib/middleman-core/preview_server.rb
index b70e9c99..1a3d220e 100644
--- a/middleman-core/lib/middleman-core/preview_server.rb
+++ b/middleman-core/lib/middleman-core/preview_server.rb
@@ -143,7 +143,7 @@ module Middleman
 
         app = ::Middleman::Application.new do
           config[:cli_options] = cli_options.each_with_object({}) do |(k, v), sum|
-            sum[k] = v unless v == :undefined
+            sum[k] = v
           end
 
           ready do
@@ -160,6 +160,9 @@ module Middleman
                                     path: root,
                                     only: match_against
 
+              # Hack around bower_components in root.
+              watcher.listener.ignore(/^bower_components/)
+
               # Hack around node_modules in root.
               watcher.listener.ignore(/^node_modules/)
 
@@ -204,7 +207,7 @@ module Middleman
       end
 
       def possible_from_cli(key, config)
-        if @cli_options[key] && @cli_options[key] != :undefined
+        if @cli_options[key]
           @cli_options[key]
         else
           config[key]
diff --git a/middleman-core/lib/middleman-core/rack.rb b/middleman-core/lib/middleman-core/rack.rb
index 797d3bf4..640dbad9 100644
--- a/middleman-core/lib/middleman-core/rack.rb
+++ b/middleman-core/lib/middleman-core/rack.rb
@@ -93,6 +93,9 @@ module Middleman
       request_path = ::Middleman::Util.full_path(request_path, @middleman)
       full_request_path = File.join(env['SCRIPT_NAME'], request_path) # Path including rack mount
 
+      # Run before callbacks
+      @middleman.execute_callbacks(:before)
+
       # Get the resource object for this path
       resource = @middleman.sitemap.find_resource_by_destination_path(request_path.gsub(' ', '%20'))
 
@@ -130,9 +133,15 @@ module Middleman
 
     # Immediately send static file
     def send_file(resource, env)
-      file      = ::Rack::File.new nil
-      file.path = resource.file_descriptor[:full_path]
-      response = file.serving(env)
+      file     = ::Rack::File.new nil
+      path     = resource.file_descriptor[:full_path]
+      if !file.respond_to?(:path=)
+        request  = ::Rack::Request.new(env)
+        response = file.serving(request, path)
+      else
+        file.path = path
+        response = file.serving(env)
+      end
       status = response[0]
       response[1]['Content-Encoding'] = 'gzip' if %w(.svgz .gz).include?(resource.ext)
       # Do not set Content-Type if status is 1xx, 204, 205 or 304, otherwise
diff --git a/middleman-core/lib/middleman-core/renderers/redcarpet.rb b/middleman-core/lib/middleman-core/renderers/redcarpet.rb
index 1542489c..b2171f22 100644
--- a/middleman-core/lib/middleman-core/renderers/redcarpet.rb
+++ b/middleman-core/lib/middleman-core/renderers/redcarpet.rb
@@ -3,7 +3,7 @@ require 'active_support/core_ext/module/attribute_accessors'
 
 module Middleman
   module Renderers
-    class RedcarpetTemplate < ::Tilt::RedcarpetTemplate::Redcarpet2
+    class RedcarpetTemplate < ::Tilt::RedcarpetTemplate
       # because tilt has decided to convert these
       # in the wrong direction
       ALIASES = {
diff --git a/middleman-core/lib/middleman-core/renderers/sass_functions.rb b/middleman-core/lib/middleman-core/renderers/sass_functions.rb
index dbe4c015..8db5707b 100644
--- a/middleman-core/lib/middleman-core/renderers/sass_functions.rb
+++ b/middleman-core/lib/middleman-core/renderers/sass_functions.rb
@@ -105,10 +105,8 @@ module Middleman
   end
 end
 
-SASS_MODULE = if defined?(::SassC)
-  ::SassC
-else
-  ::Sass
+if defined?(::SassC)
+  ::SassC::Script::Functions.send :include, ::Middleman::Sass::Functions
+elsif defined?(::Sass)
+  ::Sass::Script::Functions.send :include, ::Middleman::Sass::Functions
 end
-
-SASS_MODULE::Script::Functions.send :include, ::Middleman::Sass::Functions
diff --git a/middleman-core/lib/middleman-core/renderers/slim.rb b/middleman-core/lib/middleman-core/renderers/slim.rb
index 16640f4a..818382ad 100644
--- a/middleman-core/lib/middleman-core/renderers/slim.rb
+++ b/middleman-core/lib/middleman-core/renderers/slim.rb
@@ -12,13 +12,9 @@ class ::Slim::Template
 
   def initialize(file, line, opts, &block)
     if opts.key?(:context)
-      context_hack = {
-        context: opts[:context]
-      }
-
       ::Slim::Embedded::SassEngine.disable_option_validator!
       %w(sass scss markdown).each do |engine|
-        ::Slim::Embedded.options[engine.to_sym] = context_hack
+        (::Slim::Embedded.options[engine.to_sym] ||= {})[:context] = opts[:context]
       end
     end
 
diff --git a/middleman-core/lib/middleman-core/sitemap/extensions/ignores.rb b/middleman-core/lib/middleman-core/sitemap/extensions/ignores.rb
index dfa80304..0367c64a 100644
--- a/middleman-core/lib/middleman-core/sitemap/extensions/ignores.rb
+++ b/middleman-core/lib/middleman-core/sitemap/extensions/ignores.rb
@@ -14,16 +14,31 @@ module Middleman
         Contract Or[String, Regexp, Proc] => RespondTo[:execute_descriptor]
         def ignore(path=nil, &block)
           @app.sitemap.invalidate_resources_not_ignored_cache!
-          IgnoreDescriptor.new(path, block)
+
+          if path.is_a? Regexp
+            RegexpIgnoreDescriptor.new(path)
+          elsif path.is_a? String
+            path_clean = ::Middleman::Util.normalize_path(path)
+
+            if path_clean.include?('*') # It's a glob
+              GlobIgnoreDescriptor.new(path_clean)
+            else
+              StringIgnoreDescriptor.new(path_clean)
+            end
+          elsif block
+            BlockIgnoreDescriptor.new(nil, block)
+          else
+            IgnoreDescriptor.new(path, block)
+          end
         end
 
         IgnoreDescriptor = Struct.new(:path, :block) do
           def execute_descriptor(_app, resources)
             resources.map do |r|
               # Ignore based on the source path (without template extensions)
-              if ignored?(r.path)
+              if ignored?(r.normalized_path)
                 r.ignore!
-              elsif !r.is_a?(ProxyResource) && r.file_descriptor && ignored?(r.file_descriptor[:relative_path].to_s)
+              elsif !r.is_a?(ProxyResource) && r.file_descriptor && ignored?(r.file_descriptor.normalized_relative_path)
                 # This allows files to be ignored by their source file name (with template extensions)
                 r.ignore!
               end
@@ -33,27 +48,38 @@ module Middleman
           end
 
           def ignored?(match_path)
-            match_path = ::Middleman::Util.normalize_path(match_path)
+            raise NotImplementedError
+          end
+        end
 
-            if path.is_a? Regexp
-              match_path =~ path
-            elsif path.is_a? String
-              path_clean = ::Middleman::Util.normalize_path(path)
+        class RegexpIgnoreDescriptor < IgnoreDescriptor
+          def ignored?(match_path)
+            match_path =~ path
+          end
+        end
 
-              if path_clean.include?('*') # It's a glob
-                if defined?(::File::FNM_EXTGLOB)
-                  ::File.fnmatch(path_clean, match_path, ::File::FNM_EXTGLOB)
-                else
-                  ::File.fnmatch(path_clean, match_path)
-                end
-              else
-                match_path == path_clean
-              end
-            elsif block
-              block.call(match_path)
+        class GlobIgnoreDescriptor < IgnoreDescriptor
+          def ignored?(match_path)
+            if defined?(::File::FNM_EXTGLOB)
+              ::File.fnmatch(path, match_path, ::File::FNM_EXTGLOB)
+            else
+              ::File.fnmatch(path, match_path)
             end
           end
         end
+
+        class StringIgnoreDescriptor < IgnoreDescriptor
+          def ignored?(match_path)
+            match_path == path
+          end
+        end
+
+        class BlockIgnoreDescriptor < IgnoreDescriptor
+          def ignored?(match_path)
+            block.call(match_path)
+          end
+        end
+
       end
     end
   end
diff --git a/middleman-core/lib/middleman-core/sitemap/extensions/proxies.rb b/middleman-core/lib/middleman-core/sitemap/extensions/proxies.rb
index b11e02eb..42098ae8 100644
--- a/middleman-core/lib/middleman-core/sitemap/extensions/proxies.rb
+++ b/middleman-core/lib/middleman-core/sitemap/extensions/proxies.rb
@@ -47,7 +47,7 @@ module Middleman
           )
 
           if should_ignore
-            d = ::Middleman::Sitemap::Extensions::Ignores::IgnoreDescriptor.new(target)
+            d = ::Middleman::Sitemap::Extensions::Ignores::StringIgnoreDescriptor.new(target)
             d.execute_descriptor(app, resources)
           end
 
diff --git a/middleman-core/lib/middleman-core/sitemap/extensions/redirects.rb b/middleman-core/lib/middleman-core/sitemap/extensions/redirects.rb
index 48ede6a0..3ff15718 100644
--- a/middleman-core/lib/middleman-core/sitemap/extensions/redirects.rb
+++ b/middleman-core/lib/middleman-core/sitemap/extensions/redirects.rb
@@ -53,8 +53,7 @@ module Middleman
         def render(*)
           url = ::Middleman::Util.url_for(@store.app, @request_path,
                                           relative: false,
-                                          find_resource: true
-                                         )
+                                          find_resource: true)
 
           if output
             output.call(path, url)
diff --git a/middleman-core/lib/middleman-core/sitemap/extensions/request_endpoints.rb b/middleman-core/lib/middleman-core/sitemap/extensions/request_endpoints.rb
index 85601960..ede1cc64 100644
--- a/middleman-core/lib/middleman-core/sitemap/extensions/request_endpoints.rb
+++ b/middleman-core/lib/middleman-core/sitemap/extensions/request_endpoints.rb
@@ -9,13 +9,14 @@ module Middleman
         # Expose `endpoint`
         expose_to_config :endpoint
 
-        EndpointDescriptor = Struct.new(:path, :block) do
+        EndpointDescriptor = Struct.new(:path, :request_path, :block) do
           def execute_descriptor(app, resources)
-            r = ::Middleman::Sitemap::CallbackResource.new(
+            r = EndpointResource.new(
               app.sitemap,
               path,
-              &block
+              request_path
             )
+            r.output = block if block
 
             resources + [r]
           end
@@ -23,10 +24,43 @@ module Middleman
 
         # Setup a proxy from a path to a target
         # @param [String] path
+        # @param [Hash] opts The :path value gives a request path if it
         # differs from the output path
-        Contract String, Proc => EndpointDescriptor
-        def endpoint(path, &block)
-          EndpointDescriptor.new(path, block)
+        Contract String, Or[{ path: String }, Proc] => EndpointDescriptor
+        def endpoint(path, opts={}, &block)
+          if block_given?
+            EndpointDescriptor.new(path, path, block)
+          else
+            EndpointDescriptor.new(path, opts[:path] || path, nil)
+          end
+        end
+      end
+
+      class EndpointResource < ::Middleman::Sitemap::Resource
+        Contract Maybe[Proc]
+        attr_accessor :output
+
+        def initialize(store, path, request_path)
+          super(store, path)
+          @request_path = ::Middleman::Util.normalize_path(request_path)
+        end
+
+        Contract String
+        attr_reader :request_path
+
+        Contract Bool
+        def template?
+          true
+        end
+
+        Contract Args[Any] => String
+        def render(*)
+          return output.call if output
+        end
+
+        Contract Bool
+        def ignored?
+          false
         end
       end
     end
diff --git a/middleman-core/lib/middleman-core/sitemap/resource.rb b/middleman-core/lib/middleman-core/sitemap/resource.rb
index f4a33f83..f3619873 100644
--- a/middleman-core/lib/middleman-core/sitemap/resource.rb
+++ b/middleman-core/lib/middleman-core/sitemap/resource.rb
@@ -3,7 +3,6 @@ require 'middleman-core/sitemap/extensions/traversal'
 require 'middleman-core/file_renderer'
 require 'middleman-core/template_renderer'
 require 'middleman-core/contracts'
-require 'middleman-core/inline_url_rewriter'
 
 module Middleman
   # Sitemap namespace
@@ -40,26 +39,24 @@ module Middleman
       attr_reader :metadata
 
       attr_accessor :ignored
-      attr_accessor :filters
 
       # Initialize resource with parent store and URL
       # @param [Middleman::Sitemap::Store] store
       # @param [String] path
       # @param [String] source
-      Contract IsA['Middleman::Sitemap::Store'], String, Maybe[Any] => Any
-      def initialize(store, path, source_file=nil)
+      Contract IsA['Middleman::Sitemap::Store'], String, Maybe[Or[IsA['Middleman::SourceFile'], String]] => Any
+      def initialize(store, path, source=nil)
         @store       = store
         @app         = @store.app
         @path        = path
         @ignored     = false
-        @filters     = []
 
-        source_file = Pathname(source_file) if source_file && source_file.is_a?(String)
+        source = Pathname(source) if source && source.is_a?(String)
 
-        @file_descriptor = if source_file && source_file.is_a?(Pathname)
-          ::Middleman::SourceFile.new(source_file.relative_path_from(@app.source_dir), source_file, @app.source_dir, Set.new([:source]), 0)
+        @file_descriptor = if source && source.is_a?(Pathname)
+          ::Middleman::SourceFile.new(source.relative_path_from(@app.source_dir), source, @app.source_dir, Set.new([:source]), 0)
         else
-          source_file
+          source
         end
 
         @destination_path = @path
@@ -83,14 +80,14 @@ module Middleman
 
       # Backwards compatible method for turning descriptor into a string.
       # @return [String]
-      Contract String
+      Contract Maybe[String]
       def source_file
         file_descriptor && file_descriptor[:full_path].to_s
       end
 
       Contract Or[Symbol, String, Fixnum]
       def page_id
-        metadata[:page][:id] || destination_path
+        metadata[:page][:id] || make_implicit_page_id(destination_path)
       end
 
       # Merge in new metadata specific to this resource.
@@ -141,45 +138,8 @@ module Middleman
 
       # Render this resource
       # @return [String]
-      # Contract Maybe[Hash], Maybe[Hash], Maybe[Proc] => String
-      def render(opts={}, locs={})
-        body = render_without_filters(opts, locs)
-
-        return body if @filters.empty?
-
-        sortable_filters = @filters.select { |f| f.respond_to?(:filter_name) }.sort do |a, b|
-          if b.after_filter == a.filter_name
-            1
-          else
-            -1
-          end
-        end.reverse
-
-        n = 0
-        sorted_filters = @filters.sort_by do |m|
-          n += 1
-          idx = sortable_filters.index(m)
-
-          [idx.nil? ? 0 : idx, n]
-        end
-
-        sorted_filters.reduce(body) do |output, filter|
-          if block_given? && !yield(filter)
-            output
-          elsif filter.respond_to?(:execute_filter)
-            filter.execute_filter(output)
-          elsif filter.respond_to?(:call)
-            filter.call(output)
-          else
-            output
-          end
-        end
-      end
-
-      # Render this resource without content filters
-      # @return [String]
       Contract Hash, Hash => String
-      def render_without_filters(opts={}, locs={})
+      def render(opts={}, locs={})
         return ::Middleman::FileRenderer.new(@app, file_descriptor[:full_path].to_s).template_data_for_file unless template?
 
         md   = metadata
@@ -191,7 +151,7 @@ module Middleman
         opts[:layout] = false if !opts.key?(:layout) && !@app.config.extensions_with_layout.include?(ext)
 
         renderer = ::Middleman::TemplateRenderer.new(@app, file_descriptor[:full_path].to_s)
-        renderer.render(locs, opts).to_str
+        renderer.render(locs, opts)
       end
 
       # A path without the directory index - so foo/index.html becomes
@@ -237,17 +197,47 @@ module Middleman
         options[:content_type] || ::Rack::Mime.mime_type(ext, nil)
       end
 
+      # The normalized source path of this resource (relative to the source directory,
+      # without template extensions)
+      # @return [String]
+      def normalized_path
+        @normalized_path ||= ::Middleman::Util.normalize_path @path
+      end
+
       def to_s
         "#<#{self.class} path=#{@path}>"
       end
       alias inspect to_s # Ruby 2.0 calls inspect for NoMethodError instead of to_s
+
+      protected
+
+      # Makes a page id based on path (when not otherwise given)
+      #
+      # Removes .html extension and potential leading slashes or dots
+      # eg. "foo/bar/baz.foo.html" => "foo/bar/baz.foo"
+      Contract String => String
+      def make_implicit_page_id(path)
+        @id ||= begin
+          if prok = @app.config[:page_id_generator]
+            return prok.call(path)
+          end
+
+          basename = if ext == ".html"
+                       File.basename(path, ext)
+                     else
+                       File.basename(path)
+                     end
+
+          # Remove leading dot or slash if present
+          File.join(File.dirname(path), basename).gsub(/^\.?\//, '')
+        end
+      end
     end
 
     class StringResource < Resource
-      Contract IsA['Middleman::Sitemap::Store'], String, Maybe[Or[String, Proc]] => Any
-      def initialize(store, path, contents)
+      def initialize(store, path, contents=nil, &block)
         @request_path = path
-        @contents = contents
+        @contents = block_given? ? block : contents
         super(store, path)
       end
 
@@ -256,28 +246,7 @@ module Middleman
       end
 
       def render(*)
-        @contents
-      end
-
-      def binary?
-        false
-      end
-    end
-
-    class CallbackResource < Resource
-      Contract IsA['Middleman::Sitemap::Store'], String, Proc => Any
-      def initialize(store, path, &block)
-        @request_path = path
-        @contents = block
-        super(store, path)
-      end
-
-      def template?
-        true
-      end
-
-      def render(*)
-        @contents.call
+        @contents.respond_to?(:call) ? @contents.call : @contents
       end
 
       def binary?
diff --git a/middleman-core/lib/middleman-core/sitemap/store.rb b/middleman-core/lib/middleman-core/sitemap/store.rb
index 47e678ba..25913c7e 100644
--- a/middleman-core/lib/middleman-core/sitemap/store.rb
+++ b/middleman-core/lib/middleman-core/sitemap/store.rb
@@ -102,7 +102,7 @@ module Middleman
       # @param [Numeric] priority Sets the order of this resource list manipulator relative to the rest. By default this is 50, and manipulators run in the order they are registered, but if a priority is provided then this will run ahead of or behind other manipulators.
       # @param [Symbol] custom_name The method name to execute.
       # @return [void]
-      Contract Symbol, RespondTo[:manipulate_resource_list], Maybe[Num], Maybe[Symbol] => Any
+      Contract Symbol, RespondTo[:manipulate_resource_list], Maybe[Num, Bool], Maybe[Symbol] => Any
       def register_resource_list_manipulator(name, manipulator, priority=50, custom_name=nil)
         # The third argument used to be a boolean - handle those who still pass one
         priority = 50 unless priority.is_a? Numeric
diff --git a/middleman-core/lib/middleman-core/sources.rb b/middleman-core/lib/middleman-core/sources.rb
index f0d3cc91..ced46227 100644
--- a/middleman-core/lib/middleman-core/sources.rb
+++ b/middleman-core/lib/middleman-core/sources.rb
@@ -8,6 +8,10 @@ module Middleman
       ::Middleman::Sources.file_cache[full_path] ||= {}
       ::Middleman::Sources.file_cache[full_path][version] ||= ::File.read(full_path)
     end
+
+    def normalized_relative_path
+      @normalized_relative_path ||= ::Middleman::Util.normalize_path relative_path.to_s
+    end
   end
 
   # Sources handle multiple on-disk collections of files which make up
@@ -52,15 +56,13 @@ module Middleman
     # @param [Hash] options Global options.
     # @param [Array] watchers Default watchers.
     Contract IsA['Middleman::Application'], Maybe[Hash], Maybe[Array] => Any
-    def initialize(app, options={}, watchers=[])
+    def initialize(app, _options={}, watchers=[])
       @app = app
       @watchers = watchers
       @sorted_watchers = @watchers.dup.freeze
 
       ::Middleman::Sources.file_cache = {}
 
-      @options = options
-
       # Set of procs wanting to be notified of changes
       @on_change_callbacks = ::Hamster::Vector.empty
 
@@ -168,7 +170,7 @@ module Middleman
     # @return [Middleman::Sources]
     Contract Symbol => ::Middleman::Sources
     def by_type(type)
-      self.class.new @app, @options, watchers.select { |d| d.type == type }
+      self.class.new @app, nil, watchers.select { |d| d.type == type }
     end
 
     # Get all files for this collection of watchers.
diff --git a/middleman-core/lib/middleman-core/sources/source_watcher.rb b/middleman-core/lib/middleman-core/sources/source_watcher.rb
index 9852e223..8e3a3550 100644
--- a/middleman-core/lib/middleman-core/sources/source_watcher.rb
+++ b/middleman-core/lib/middleman-core/sources/source_watcher.rb
@@ -75,9 +75,10 @@ module Middleman
       @ignored = options.fetch(:ignored, proc { false })
       @only = Array(options.fetch(:only, []))
 
-      @disable_watcher = app.build? || @parent.options.fetch(:disable_watcher, false)
-      @force_polling = @parent.options.fetch(:force_polling, false)
-      @latency = @parent.options.fetch(:latency, nil)
+      @disable_watcher = app.build?
+      @force_polling = false
+      @latency = nil
+      @wait_for_delay = nil
 
       @listener = nil
 
@@ -95,13 +96,20 @@ module Middleman
     def update_path(directory)
       @directory = Pathname(File.expand_path(directory, app.root))
 
-      stop_listener! if @listener
-
-      update([], @files.values.map { |source_file| source_file[:full_path] })
+      without_listener_running do
+        update([], @files.values.map { |source_file| source_file[:full_path] })
+      end
 
       poll_once!
+    end
 
-      listen! unless @disable_watcher
+    def update_config(options={})
+      without_listener_running do
+        @disable_watcher = options.fetch(:disable_watcher, false)
+        @force_polling = options.fetch(:force_polling, false)
+        @latency = options.fetch(:latency, nil)
+        @wait_for_delay = options.fetch(:wait_for_delay, nil)
+      end
     end
 
     # Stop watching.
@@ -160,10 +168,10 @@ module Middleman
 
       config = {
         force_polling: @force_polling,
-        wait_for_delay: 0.5
       }
 
-      config[:latency] = @latency if @latency
+      config[:wait_for_delay] = @wait_for_delay.try(:to_f) || 0.5
+      config[:latency] = @latency.to_f if @latency
 
       @listener = ::Listen.to(@directory.to_s, config, &method(:on_listener_change))
 
@@ -199,7 +207,7 @@ module Middleman
     Contract ArrayOf[Pathname]
     def poll_once!
       updated = ::Middleman::Util.all_files_under(@directory.to_s, &method(:should_not_recurse?))
-      removed = @files.keys.reject { |p| updated.include?(p) }
+      removed = @files.keys - updated
 
       result = update(updated, removed)
 
@@ -343,5 +351,20 @@ module Middleman
         @only.any? { |reg| file[:relative_path].to_s =~ reg }
       end
     end
+
+    private
+
+    def without_listener_running
+      listener_running = @listener && @listener.processing?
+
+      stop_listener! if listener_running
+
+      yield
+
+      if listener_running
+        poll_once!
+        listen!
+      end
+    end
   end
 end
diff --git a/middleman-core/lib/middleman-core/template_context.rb b/middleman-core/lib/middleman-core/template_context.rb
index 0842b846..5efd8c41 100644
--- a/middleman-core/lib/middleman-core/template_context.rb
+++ b/middleman-core/lib/middleman-core/template_context.rb
@@ -127,30 +127,34 @@ module Middleman
     # @return [String]
     Contract String, Maybe[Bool] => Maybe[IsA['Middleman::SourceFile']]
     def locate_partial(partial_path, try_static=true)
-      return unless resource = sitemap.find_resource_by_destination_path(current_path)
-
-      # Look for partials relative to the current path
-      current_dir = resource.file_descriptor[:relative_path].dirname
-      non_root = partial_path.to_s.sub(/^\//, '')
-      relative_dir = current_dir + Pathname(non_root)
-
-      non_root_no_underscore = non_root.sub(/^_/, '').sub(/\/_/, '/')
-      relative_dir_no_underscore = current_dir + Pathname(non_root_no_underscore)
-
       partial_file = nil
+      lookup_stack = []
+      non_root     = partial_path.to_s.sub(/^\//, '')
+      non_root_no_underscore = non_root.sub(/^_/, '').sub(/\/_/, '/')
 
-      [
-        [relative_dir.to_s, { preferred_engine: resource.file_descriptor[:relative_path].extname[1..-1].to_sym }],
-        [non_root],
-        [non_root, { try_static: try_static }],
-        [relative_dir_no_underscore.to_s, { try_static: try_static }],
-        [non_root_no_underscore, { try_static: try_static }]
-      ].each do |args|
+      if resource = current_resource
+        current_dir  = resource.file_descriptor[:relative_path].dirname
+        relative_dir = current_dir + Pathname(non_root)
+        relative_dir_no_underscore = current_dir + Pathname(non_root_no_underscore)
+      end
+
+      lookup_stack.push [relative_dir.to_s,
+                         { preferred_engine: resource.file_descriptor[:relative_path]
+                           .extname[1..-1].to_sym }] if relative_dir
+      lookup_stack.push [non_root]
+      lookup_stack.push [non_root,
+                         { try_static: try_static }]
+      lookup_stack.push [relative_dir_no_underscore.to_s,
+                         { try_static: try_static }] if relative_dir_no_underscore
+      lookup_stack.push [non_root_no_underscore,
+                         { try_static: try_static }]
+
+      lookup_stack.each do |args|
         partial_file = ::Middleman::TemplateRenderer.resolve_template(@app, *args)
         break if partial_file
       end
 
-      partial_file || nil
+      partial_file
     end
 
     def current_path
diff --git a/middleman-core/lib/middleman-core/template_renderer.rb b/middleman-core/lib/middleman-core/template_renderer.rb
index 0dcf2af8..8100a56d 100644
--- a/middleman-core/lib/middleman-core/template_renderer.rb
+++ b/middleman-core/lib/middleman-core/template_renderer.rb
@@ -64,9 +64,7 @@ module Middleman
         extension_class = ::Middleman::Util.tilt_class(options[:preferred_engine])
 
         # Get a list of extensions for a preferred engine
-        preferred_engines += ::Tilt.mappings.select do |_, engines|
-          engines.include? extension_class
-        end.keys
+        preferred_engines += ::Tilt.default_mapping.extensions_for(extension_class)
       end
 
       preferred_engines << '*'
diff --git a/middleman-core/lib/middleman-core/util/binary.rb b/middleman-core/lib/middleman-core/util/binary.rb
index 71e584d1..be131965 100644
--- a/middleman-core/lib/middleman-core/util/binary.rb
+++ b/middleman-core/lib/middleman-core/util/binary.rb
@@ -47,14 +47,13 @@ module Middleman
     # @return [Boolean]
     Contract String => Bool
     def nonbinary_mime?(mime)
-      case
-      when mime.start_with?('text/')
+      if mime.start_with?('text/')
         true
-      when mime.include?('xml') && !mime.include?('officedocument')
+      elsif mime.include?('xml') && !mime.include?('officedocument')
         true
-      when mime.include?('json')
+      elsif mime.include?('json')
         true
-      when mime.include?('javascript')
+      elsif mime.include?('javascript')
         true
       else
         false
diff --git a/middleman-core/lib/middleman-core/util/files.rb b/middleman-core/lib/middleman-core/util/files.rb
index 607b3bd5..3d185cea 100644
--- a/middleman-core/lib/middleman-core/util/files.rb
+++ b/middleman-core/lib/middleman-core/util/files.rb
@@ -56,8 +56,10 @@ module Middleman
 
     Contract String => String
     def step_through_extensions(path)
-      while ext = File.extname(path)
-        break if ext.empty? || !::Middleman::Util.tilt_class(ext)
+      while ::Middleman::Util.tilt_class(path)
+        ext = ::File.extname(path)
+        break if ext.empty?
+
         yield ext if block_given?
 
         # Strip templating extensions as long as Tilt knows them
diff --git a/middleman-core/lib/middleman-core/util/paths.rb b/middleman-core/lib/middleman-core/util/paths.rb
index b6543612..2e229392 100644
--- a/middleman-core/lib/middleman-core/util/paths.rb
+++ b/middleman-core/lib/middleman-core/util/paths.rb
@@ -1,8 +1,8 @@
 # Core Pathname library used for traversal
 require 'pathname'
 require 'uri'
+require 'addressable/uri'
 require 'memoist'
-require 'addressable'
 require 'tilt'
 
 require 'middleman-core/contracts'
@@ -25,18 +25,16 @@ module Middleman
     def tilt_class(path)
       ::Tilt[path]
     end
-    # memoize :tilt_class
+    memoize :tilt_class
 
     # Normalize a path to not include a leading slash
     # @param [String] path
     # @return [String]
-    Contract Any => String
+    Contract String => String
     def normalize_path(path)
-      return path unless path.is_a?(String)
-
-      # The tr call works around a bug in Ruby's Unicode handling
+     # The tr call works around a bug in Ruby's Unicode handling
       ::URI.decode(path).sub(%r{^/}, '').tr('', '')
-    end
+     end
     memoize :normalize_path
 
     # This is a separate method from normalize_path in case we
@@ -113,14 +111,16 @@ module Middleman
         raise ArgumentError, '#asset_url must be run in a context with current_resource if relative: true'
       end
 
-      uri = URI(path)
+      uri = ::Middleman::Util.parse_uri(path)
       path = uri.path
 
       # Ensure the url we pass into find_resource_by_destination_path is not a
       # relative path, since it only takes absolute url paths.
       dest_path = url_for(app, path, options.merge(relative: false))
 
-      result = if resource = app.sitemap.find_resource_by_destination_path(dest_path)
+      result = if resource = app.sitemap.find_resource_by_path(dest_path)
+        resource.url
+      elsif resource = app.sitemap.find_resource_by_destination_path(dest_path)
         resource.url
       else
         path = ::File.join(prefix, path)
@@ -131,9 +131,15 @@ module Middleman
         end
       end
 
-      final_result = ::URI.encode(relative_path_from_resource(options[:current_resource], result, options[:relative]))
+      final_result = ::Addressable::URI.encode(
+        relative_path_from_resource(
+          options[:current_resource],
+          result,
+          options[:relative]
+        )
+      )
 
-      result_uri = URI(final_result)
+      result_uri = ::Middleman::Util.parse_uri(final_result)
       result_uri.query = uri.query
       result_uri.fragment = uri.fragment
       result_uri.to_s
@@ -146,7 +152,8 @@ module Middleman
     def url_for(app, path_or_resource, options={})
       if path_or_resource.is_a?(String) || path_or_resource.is_a?(Symbol)
         r = app.sitemap.find_resource_by_page_id(path_or_resource)
-        path_or_resource = r if r
+
+        path_or_resource = r ? r : path_or_resource.to_s
       end
 
       # Handle Resources and other things which define their own url method
@@ -158,8 +165,8 @@ module Middleman
 
       # Try to parse URL
       begin
-        uri = URI(url)
-      rescue ::URI::InvalidURIError
+        uri = ::Middleman::Util.parse_uri(url)
+      rescue ::Addressable::URI::InvalidURIError
         # Nothing we can do with it, it's not really a URI
         return url
       end
@@ -202,7 +209,13 @@ module Middleman
 
       if resource
         uri.path = if this_resource
-          ::URI.encode(relative_path_from_resource(this_resource, resource_url, effective_relative))
+          ::Addressable::URI.encode(
+            relative_path_from_resource(
+              this_resource,
+              resource_url,
+              effective_relative
+            )
+          )
         else
           resource_url
         end
@@ -280,16 +293,15 @@ module Middleman
     # @return [Boolean] Whether the path matches the matcher
     Contract PATH_MATCHER, String => Bool
     def path_match(matcher, path)
-      case
-      when matcher.is_a?(String)
+      if matcher.is_a?(String)
         if matcher.include? '*'
           ::File.fnmatch(matcher, path)
         else
           path == matcher
         end
-      when matcher.respond_to?(:match)
+      elsif matcher.respond_to?(:match)
         !!(path =~ matcher)
-      when matcher.respond_to?(:call)
+      elsif matcher.respond_to?(:call)
         matcher.call(path)
       else
         ::File.fnmatch(matcher.to_s, path)
diff --git a/middleman-core/lib/middleman-core/util/rack.rb b/middleman-core/lib/middleman-core/util/rack.rb
index 6783ff2d..2459052b 100644
--- a/middleman-core/lib/middleman-core/util/rack.rb
+++ b/middleman-core/lib/middleman-core/util/rack.rb
@@ -6,9 +6,22 @@ module Middleman
 
     module_function
 
-    Contract String, String, SetOf[String], IsA['::Middleman::Application'], Proc => String
+    # Extract the text of a Rack response as a string.
+    # Useful for extensions implemented as Rack middleware.
+    # @param response The response from #call
+    # @return [String] The whole response as a string.
+    Contract RespondTo[:each] => String
+    def extract_response_text(response)
+      # The rack spec states all response bodies must respond to each
+      result = ''
+      response.each do |part, _|
+        result << part
+      end
+      result
+    end
+
+    Contract String, String, ArrayOf[String], IsA['::Middleman::Application'], Proc => String
     def rewrite_paths(body, path, exts, app, &_block)
-      exts = exts.sort_by(&:length).reverse
       matcher = /([\'\"\(,]\s*|# sourceMappingURL=)([^\s\'\"\)\(>]+(#{::Regexp.union(exts)}))/
 
       url_fn_prefix = 'url('
diff --git a/middleman-core/lib/middleman-core/version.rb b/middleman-core/lib/middleman-core/version.rb
index 4fe534de..7b1bf403 100644
--- a/middleman-core/lib/middleman-core/version.rb
+++ b/middleman-core/lib/middleman-core/version.rb
@@ -1,5 +1,5 @@
 module Middleman
   # Current Version
   # @return [String]
-  VERSION = '4.2.0'.freeze unless const_defined?(:VERSION)
+  VERSION = '4.1.14'.freeze unless const_defined?(:VERSION)
 end
diff --git a/middleman-core/middleman-core.gemspec b/middleman-core/middleman-core.gemspec
index fde0883c..38df7be7 100644
--- a/middleman-core/middleman-core.gemspec
+++ b/middleman-core/middleman-core.gemspec
@@ -16,19 +16,20 @@ Gem::Specification.new do |s|
   s.files        = `git ls-files -z`.split("\0")
   s.test_files   = `git ls-files -z -- {fixtures,features}/*`.split("\0")
   s.require_path = 'lib'
-  s.required_ruby_version = '>= 2.0.0'
+  s.required_ruby_version = '>= 2.2.0'
 
   # Core
   s.add_dependency('bundler', ['~> 1.1'])
-  s.add_dependency('rack', ['>= 1.4.5', '< 2.0'])
-  s.add_dependency('tilt', ['~> 1.4.1'])
+  s.add_dependency('rack', ['>= 1.4.5', '< 3'])
+  s.add_dependency('tilt', ['~> 2.0'])
   s.add_dependency('erubis')
   s.add_dependency('fast_blank')
   s.add_dependency('parallel')
   s.add_dependency('servolux')
+  s.add_dependency('dotenv')
 
   # Helpers
-  s.add_dependency('activesupport', ['~> 4.2'])
+  s.add_dependency('activesupport', ['>= 4.2', '< 5.1'])
   s.add_dependency('padrino-helpers', ['~> 0.13.0'])
   s.add_dependency("addressable", ["~> 2.3"])
   s.add_dependency('memoist', ['~> 0.14'])
@@ -37,7 +38,7 @@ Gem::Specification.new do |s|
   s.add_dependency('listen', ['~> 3.0.0'])
 
   # Tests
-  s.add_dependency("capybara", ["~> 2.5.0"])
+  s.add_development_dependency("capybara", ["~> 2.5.0"])
 
   # i18n
   s.add_dependency('i18n', ['~> 0.7.0'])
diff --git a/middleman-core/spec/middleman-core/util_spec.rb b/middleman-core/spec/middleman-core/util_spec.rb
index ea9bbd88..9c429145 100644
--- a/middleman-core/spec/middleman-core/util_spec.rb
+++ b/middleman-core/spec/middleman-core/util_spec.rb
@@ -162,6 +162,13 @@ describe Middleman::Util do
       expect( Middleman::Util.asset_url( @mm, '/how/about/that.html' ) ).to eq '/how/about/that/'
     end
 
+    it "returns a resource url when asset_hash is on" do
+      Given.fixture 'asset-hash-app'
+      @mm = Middleman::Application.new
+
+      expect( Middleman::Util.asset_url( @mm, '100px.png', 'images') ).to match %r|/images/100px-[a-f0-9]+.png|
+    end
+
   end
 
   describe "::find_related_files" do
@@ -213,7 +220,7 @@ describe Middleman::Util do
 
     it "does not loop infinitely when file name is a possible templating engine" do
       expect do
-        Timeout::timeout(0.5) do
+        Timeout::timeout(3.0) do
           result = Middleman::Util.step_through_extensions("markdown.scss")
           expect(result).to eq "markdown"
         end
diff --git a/middleman/middleman.gemspec b/middleman/middleman.gemspec
index 06dd3144..a172005f 100644
--- a/middleman/middleman.gemspec
+++ b/middleman/middleman.gemspec
@@ -16,7 +16,7 @@ Gem::Specification.new do |s|
   s.files        = `git ls-files -z`.split("\0")
   s.test_files   = `git ls-files -z -- {fixtures,features}/*`.split("\0")
   s.require_path = 'lib'
-  s.required_ruby_version = '>= 2.0.0'
+  s.required_ruby_version = '>= 2.2.0'
 
   s.add_dependency('middleman-core', Middleman::VERSION)
   s.add_dependency('middleman-cli', Middleman::VERSION)