patch: emit deflated binary patches (optionally)

This PR introduces binary patches.  `git-diff` will provide the "base85" encoded contents of the deflated old and new sides when specifying the `--binary` flag.  This emulates that behavior.

To do:

- [ ] Deltas:  `git-diff` will provide a binary delta between the old / new side when that would be superior to providing the deflated contents.