Wrap functionality in if tags to prevent errors

On every GitHub page but the profile overview there were errors
thrown because MutationObserver needed a node, not null
Complete rewrite in CoffeeScript
Create CoffeeScript class
Add event listner on pjax site change
Fix bug where color mapping failed
Remove pjax handler, we'll do that later
Merge pull request #6 from bahlo/coffee-script

CoffeeScript class