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
there is no enclosing else, therefore we probably can combine event[:check].has_key?(:dependencies) && event[:check][:dependencies].is_a?(Array)

as deep nested structures is really hard to understand.