Use GitHub::Markup to parse markup files

Closes #1382

app/views/refs/_tree.html.haml

@@ -43,11 +43,7 @@
           %i.icon-file
           = content.name
         .file_content.wiki
-          - if content.name =~ /\.(md|markdown)$/i
-            = preserve do
-              = markdown(content.data)
-          - else
-            = simple_format(content.data)
+          = raw GitHub::Markup.render(content.name, content.data)
 
 :javascript
   $(function(){

app/views/refs/_tree_file.html.haml

@@ -9,10 +9,9 @@
       = link_to "history", project_commits_path(@project, path: params[:path], ref: @ref), class: "btn very_small"
       = link_to "blame", blame_file_project_ref_path(@project, @ref, path: params[:path]), class: "btn very_small"
   - if file.text?
-    - if name =~ /\.(md|markdown)$/i
+    - if markup?(name)
       .file_content.wiki
-        = preserve do
-          = markdown(file.data)
+        = raw GitHub::Markup.render(name, file.data)
     - else
       .file_content.code
         - unless file.empty?