Add 'rate' command
Fix line length
Refactor to helper method on gh
Add callback rv from __call__ for show_rate

Since each `__call__` method calls the supers
call, there's no way to have all implementors
do something on function end. If this is too
invasive probably a global registry of call-
back objects would be best.
Capitalize H in GithubCommand
Define hidden callbacks argument to return show_rate
Merge pull request #6 from sbesson/rate-cmd

Rate cmd
Merge pull request #165 from joshmoore/rate-cmd

Add 'rate' command