switch to Maruku, avoid compiled extensions

lib/middleman/core_extensions/front_matter.rb

@@ -8,7 +8,8 @@ module Middleman::CoreExtensions::FrontMatter
       
       ::Tilt::register RDiscountTemplate, 'markdown', 'mkd', 'md'
       ::Tilt::register RedcarpetTemplate, 'markdown', 'mkd', 'md'
-      app.set :markdown_engine, RDiscountTemplate
+      ::Tilt::register MarukuTemplate, 'markdown', 'mkd', 'md'
+      app.set :markdown_engine, MarukuTemplate
       
       ::Tilt::register RedClothTemplate,  'textile'
       ::Tilt.prefer(RedClothTemplate)
@@ -86,7 +87,9 @@ module Middleman::CoreExtensions::FrontMatter
   class RedcarpetTemplate < ::Tilt::RedcarpetTemplate
     include Middleman::CoreExtensions::FrontMatter::YamlAware
   end
-  
+  class MarukuTemplate < ::Tilt::MarukuTemplate
+    include Middleman::CoreExtensions::FrontMatter::YamlAware
+  end
   class RedClothTemplate < ::Tilt::RedClothTemplate
     include Middleman::CoreExtensions::FrontMatter::YamlAware
   end

lib/middleman/features/blog.rb

@@ -1,5 +1,3 @@
-require "rdiscount"
-
 module Middleman
   module Features
     module Blog

lib/middleman/renderers/markdown.rb

@@ -1,7 +1,7 @@
 module Middleman::Renderers::Markdown
   class << self
     def registered(app)
-      app.set :markdown_engine, ::Tilt::RDiscountTemplate
+      app.set :markdown_engine, ::Tilt::MarukuTemplate
       app.after_configuration do
         ::Tilt.prefer(app.settings.markdown_engine)
       end