Framework for updating git gud

Whenever we add a new git hook, git gud breaks without telling us why. The current process that we have to go through to fix this is running "git gud init --force", but this will also set up the first level.

- "git gud update" to update hooks and relevant files while keeping the level the same.
- Keep track of which version of git gud a repo has been initialized to
- Notify a user if the version of their repo and their version of git gud don't match