------------------
Added
^^^^^
- `save_worktree_and_branch()` context manager.
- `process_env()` function.
- `gitdir()` generic function.
- `worktree()` generic function.
- `GitEnvInterface` for dynamic checking of interface.
Changed
^^^^^^^
- `GitEnv` is now a named tuple.
- `git()` is no longer a generic function.
- `save_worktree()` no longer saves branch.
Fixed
^^^^^
- Work around bug in `git-stash`.