cmdstate: switch to new-style classes This isn't a huge issue and isn't necessary on Python3, but we're still Python2 compatible and we should be consistent (and strongly prefer new-style classes); this is the only class that is not deriving from object that I could find.

branching: merge stable into default

docs: add example for the `prune` command Giving at least one example helps clear up the syntax, especially since most options will follow a very similar pattern.