Return args that can be used given
        the current cmd line

        rtype: command.Arg generator

def available_args(self):
        """Return args that can be used given
        the current cmd line

        rtype: command.Arg generator
        """
        used = list(self.used_args)
        logger.debug('Found used args: %s' % used)
        for arg in list(self.cmd.args.values()):
            if (arg.is_multiple or
                    arg not in used):
                yield arg
            elif (type(arg.nargs) is int and
                    arg.nargs > 1 and
                    not arg.nargs == used.count(arg)):
                yield arg