adding options for animated gif capturing (Mac only via wacaw)

Using wacaw and ffmpeg (and convert) it is possible to generate and annotate a
short animated gif for your lolcommit.  Use -a or --animate option with the
number of seconds to capture and animate.

* currently mac only
* if -a=0 (or not present) lolcommits will operate as normal
* added --fork option to allow capturing/runner to be backgrounded
* defaults to a 320x240 sized animated gif (lower filesize)
* wacaw is open source here; http://webcam-tools.sourceforge.net