Update ourself and any of our subcommands.

def depth(self, value):
        """ Update ourself and any of our subcommands. """
        for command in self.subcommands.values():
            command.depth = value + 1
            del command.argparser._defaults[self.arg_label_fmt % self._depth]
            command.argparser._defaults[self.arg_label_fmt % value] = command
        self._depth = value