Deprecate repo.Refs.Move() in favor of repo.Refs.Rename()

- [ ] Add the new `Rename()` method
- [ ] Delegate the current `Move()` implementation to `Rename()`
- [ ] Decorate `Move()` with an obsolete attribute (using the standard message pattern)
- [ ] Modify existing code so `Move()` is no longer called
#738 is a great example of a similar fix
