commandline interface #173

I'd like to be able to make a generic hook that takes as arguments essentially all of the things that are necessary to configure a pre-commit hook (repo, language, name, fileglob, etc), and do all the pre-commit-ish things with that information.

This necessitates a cli interface to the guts of pre-commit -- a command that takes all the information that configures a hook then sets it up and/or runs it.