Added "regexp" command, ported from Urban Airship pmxbot at tag 1001.
Added "regexp" command, ported from Urban Airship pmxbot at tag 1001.

The regexp command is like contains in that it watches all content,
however it allows you to monitor for a certain regexp condition and
pass a match.group() value instead of the normal message. Useful to
auto-generate links from a ticket number, for example.

yougov/pmxbot,yougov/pmxbot,yougov/pmxbot