Added Hipchat extension

This extension was originally written by @steveberryman but I'm publishing it here with his permission. (With minor modifications.)

The original is here: https://gist.github.com/steveberryman/c57dd6595429e86d6a12
@cameronbraid no one is making any nitpicks here, dude. It is a normal way to find a best solution to a problem - through discussion. Don't take it so personal, please.