More comprehensive `git status` support

It would be great if broot's `git status` mode were a more complete replacement for `git status --short`. It'd probably require expanding the git column to two characters, but it would mean one fewer reason to leave broot 😉

I'm thinking probably the ability to see new, modified, and renamed status in the index and working tree.

Start with broot's existing git status mode and compare its output with `git status --short`, focusing on index and working-tree states. Done means the mode shows new, modified, and renamed statuses in both areas, with the git column expanded as needed.

Written by the indexing model from the issue text.