Show images as raw and update the documentation.

Former-commit-id: 4f3876a2

app/helpers/gitlab_markdown_helper.rb

@@ -173,6 +173,7 @@ module GitlabMarkdownHelper
   # eg. doc/api is directory and doc/README.md is file
   def local_path(path)
     return "tree" if Tree.new(@repository, current_ref, path).entries.any?
+    return "raw" if @repository.blob_at(current_ref, path).image?
     return "blob"
   end

doc/markdown/markdown.md

@@ -326,12 +326,12 @@ Some text to show that the reference links can follow later.
     Here's our logo (hover to see the title text):
     Inline-style: 
-    ![alt text](/assets/logo-white.png "Logo Title Text 1")
+    ![alt text](assets/logo-white.png)
     Reference-style: 
-    ![alt text][logo]
-    [logo]: /assets/logo-white.png "Logo Title Text 2"
+    ![alt text1][logo]
+    [logo]: assets/logo-white.png
 Here's our logo (hover to see the title text):