Add structure of git-update command

The high level function and wrapping code has been implemented, the
actual git integration commands have not.
Adds check for a dirty working tree

Don't want to switch branches when it might be destructive.
Exit instead of returning when outside a function

Better indication of the intent.
Add gumpf to functions to allow testing

Just prevents syntax errors. Will be removed when actually implemented.
Fill out methods

The git-update command should be complete at this point. Needs testing.
Strip the current branch indicator

Not an appropriate argument to pass to git rev-list.
Also quotes the arguments in the if, to handle the case where rev-list
is blank (for whatever reason).
Merge branch 'feature/command' into develop
Adds a simple README
Only allow --rebase pulls

This will replay your work on top of the remote updates. This prevents
the leaf shaped divergence of commits, which just messes up visualizers.
Merge branch 'release/1.0.0'