Add highlighting for webidl-marked fenced code blocks

The Rouge thing for Jekyll doesn’t support webidl highlighting. So this
change causes it to use javascript highlighting for webidl-marked blocks.

Author: sideshowbarker

_plugins/rouge_webidl.rb

@@ -0,0 +1,9 @@
+require "rouge"
+
+module Rouge
+  module Lexers
+    class WebIDL < Javascript
+      tag "webidl"
+    end
+  end
+end