Feature idea: use a worktree in a temporary directory

[rcj4747]

Posting this and hopefully I'll get working on it. Once issue #2 is resolved, I'd like to specify the git repo directory to use, but do the checkout in a new worktree if git version is new enough to support them. Not sure what the overall workflow would look like, maybe an additional --use-worktree flag? lpshipit does exit before pushing to the remote, so lpshipit wouldn't be able to clean up the worktree :-/ unless it shelled out for the user to inspect the tree and push to the remote and upon exit it could clean up.

Thoughts?