Script update

* use subprocess instead of deprecated popen
* use os.chdir() with contextmanager instead of direct 'cd'
** http://docs.python.org/2/library/contextlib.html#contextlib.contextmanager
* usage formatting to be consistent with other git commands
* better color support
Add bash completion script
Update README

* Fix some typos
* Update Install section
* Reflow all text (using Vim 'gq') to make it easier to read
Merge pull request #1 from sbennett18/master

Script update, bash completion