Render markdown in snippets

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/snippets/_blob.html.haml

@@ -8,9 +8,18 @@
           = link_to "Edit", edit_snippet_path(@snippet), class: "btn btn-tiny", title: 'Edit Snippet'
           = link_to "Delete", snippet_path(@snippet), method: :delete, confirm: "Are you sure?", class: "btn btn-tiny", title: 'Delete Snippet'
         = link_to "Raw", raw_snippet_path(@snippet), class: "btn btn-tiny", target: "_blank"
-  .file-content.code
-    - unless @snippet.content.empty?
-      %div{class: user_color_scheme_class}
-        = raw @snippet.colorize(formatter: :gitlab)
+  - unless @snippet.content.empty?
+    - if gitlab_markdown?(@snippet.file_name)
+      .file-content.wiki
+        = preserve do
+          = markdown(@snippet.data)
+    - elsif markup?(@snippet.file_name)
+      .file-content.wiki
+        = raw GitHub::Markup.render(@snippet.file_name, @snippet.data)
     - else
+      .file-content.code
+        %div{class: user_color_scheme_class}
+          = raw @snippet.colorize(formatter: :gitlab)
+  - else
+    .file-content.code
       %p.nothing_here_message Empty file