Add new -sb option, which adds '--branch' to git status in addition to '...

Currently the following command:

git number -s

maps to:

git status -s

I wanted to be able to do:

git status -sb, which shows branch information in shorthand form, so I added support to git-number for this in the form of:

git number -sb

I wasn't sure where the help text was, so I couldn't update that. If you let me know I can update it for you. Let me know what you think.