hub: Import hub-2.2.9 as net/hub

hub is a command line tool that wraps git in order to extend it
with extra features and commands that make working with GitHub
easier.

$ hub clone rtomayko/tilt
# expands to:
$ git clone git://github.com/rtomayko/tilt.git

hub is best aliased as `git', so you can type `git <command>' in the
shell and get all the usual hub features.

(leot)