Asciivideo

Pull request because @jgonggrijp asked me to.

Some things to think about though:
It does pull in ffmpeg as a depend, making it linux/OS X only (?)
There might be a framerate issue on some computers.  I forget if I fixed it or not :/
This is almost certainly going to break on Windows, but I think I see a (simple) way to fix it. Stay tuned.