Make it a Pathogen plugin

I want to make it easy to load this plugin. A lot of people are using
Pathogen to control their plugins, so turning it into such seems like a
good idea.

I mostly copied stuff from @wincent and his excellent project CommandT.
It took a while for me to get the load path correctly setup, but apart
from that it wasn't too complicated. I've got a symlink locally from my
Pathogen bundle directory so that I can easily develop the plugin.

https://github.com/wincent/command-t