Implemented Rubocop

- just took a stab at running the StringLiterals cop to get a taste.

middleman-core/lib/middleman-core/core_extensions.rb

@@ -1,39 +1,39 @@
 # Rack Request
-require "middleman-core/core_extensions/request"
+require 'middleman-core/core_extensions/request'
 
 # File Change Notifier
-require "middleman-core/core_extensions/file_watcher"
+require 'middleman-core/core_extensions/file_watcher'
 
 # Custom Feature API
-require "middleman-core/core_extensions/extensions"
+require 'middleman-core/core_extensions/extensions'
 
 # Data looks at the data/ folder for YAML files and makes them available
 # to dynamic requests.
-require "middleman-core/core_extensions/data"
+require 'middleman-core/core_extensions/data'
 
 # Parse YAML from templates
-require "middleman-core/core_extensions/front_matter"
+require 'middleman-core/core_extensions/front_matter'
 
 # External helpers looks in the helpers/ folder for helper modules
-require "middleman-core/core_extensions/external_helpers"
+require 'middleman-core/core_extensions/external_helpers'
 
 # Extended version of Padrino's rendering
-require "middleman-core/core_extensions/rendering"
+require 'middleman-core/core_extensions/rendering'
 
 # Pass custom options to views
-require "middleman-core/core_extensions/routing"
+require 'middleman-core/core_extensions/routing'
 
 # Catch and show exceptions at the Rack level
-require "middleman-core/core_extensions/show_exceptions"
+require 'middleman-core/core_extensions/show_exceptions'
 
 # Setup default helpers
-require "middleman-more/core_extensions/default_helpers"
+require 'middleman-more/core_extensions/default_helpers'
 
-require "middleman-more/core_extensions/i18n"
+require 'middleman-more/core_extensions/i18n'
 
 # Compass framework
 begin
-  require "middleman-more/core_extensions/compass"
+  require 'middleman-more/core_extensions/compass'
 rescue LoadError
   $stderr.puts "Compass not installed: #{$!}"
 end
@@ -44,52 +44,52 @@ end
 
 # CacheBuster adds a query string to assets in dynamic templates to
 # avoid browser caches failing to update to your new content.
-require "middleman-more/extensions/cache_buster"
+require 'middleman-more/extensions/cache_buster'
 Middleman::Extensions::CacheBuster.register
 
 # RelativeAssets allow any asset path in dynamic templates to be either
 # relative to the root of the project or use an absolute URL.
-require "middleman-more/extensions/relative_assets"
+require 'middleman-more/extensions/relative_assets'
 Middleman::Extensions::RelativeAssets.register
 
 # AssetHost allows you to setup multiple domains to host your static
 # assets. Calls to asset paths in dynamic templates will then rotate
 # through each of the asset servers to better spread the load.
-require "middleman-more/extensions/asset_host"
+require 'middleman-more/extensions/asset_host'
 Middleman::Extensions::AssetHost.register
 
 # MinifyCss compresses CSS
-require "middleman-more/extensions/minify_css"
+require 'middleman-more/extensions/minify_css'
 Middleman::Extensions::MinifyCss.register
 
 # MinifyJavascript compresses JS
-require "middleman-more/extensions/minify_javascript"
+require 'middleman-more/extensions/minify_javascript'
 Middleman::Extensions::MinifyJavascript.register
 
 # GZIP assets and pages during build
-require "middleman-more/extensions/gzip"
+require 'middleman-more/extensions/gzip'
 Middleman::Extensions::Gzip.register
 
 # AssetHash appends a hash of the file contents to the assets filename
 # to avoid browser caches failing to update to your new content.
-require "middleman-more/extensions/asset_hash"
+require 'middleman-more/extensions/asset_hash'
 Middleman::Extensions::AssetHash.register
 
 # Provide Apache-style index.html files for directories
-require "middleman-more/extensions/directory_indexes"
+require 'middleman-more/extensions/directory_indexes'
 Middleman::Extensions::DirectoryIndexes.register
 
 # Lorem provides a handful of helpful prototyping methods to generate
 # words, paragraphs, fake images, names and email addresses.
-require "middleman-more/extensions/lorem"
+require 'middleman-more/extensions/lorem'
 
 # AutomaticImageSizes inspects the images used in your dynamic templates
 # and automatically adds width and height attributes to their HTML
 # elements.
-require "middleman-more/extensions/automatic_image_sizes"
+require 'middleman-more/extensions/automatic_image_sizes'
 Middleman::Extensions::AutomaticImageSizes.register
 
 # AutomaticAltTags uses the file name of the `image_tag` to generate
 # a default `:alt` value.
-require "middleman-more/extensions/automatic_alt_tags"
+require 'middleman-more/extensions/automatic_alt_tags'
 Middleman::Extensions::AutomaticAltTags.register