R1:1175784d5d84

PhabricatorSlug

Summary:
This is to be used in Phame so the logic is shared where possible. The change has three main things going on

- broke out functionality from PhrictionDocument that isn't Phriction specific.
- swept up code base to use new PhabricatorSlug class.
- altered the regex ever so slightly per discussion and http://stackoverflow.com/questions/2028022/javascript-how-to-convert-unicode-string-to-ascii

I think maybe we should punt on unicode here for quite a bit -- http://www.456bereastreet.