Uses a 'parse_build_args.py' file to add options, if found.

def bind_cli(cls, parser, group):
        """
        Uses a 'parse_build_args.py' file to add options, if found.
        """
        try:
            with open("./parse_build_args.py") as f:
                source = f.read()
        except Exception as e:
            return

        # detect what extra args have been added
        before_args = set(x.dest for x in parser._actions)

        try:
            exec source in {"parser": group}
        except Exception as e:
            print_warning("Error in ./parse_build_args.py: %s" % str(e))

        after_args = set(x.dest for x in parser._actions)
        extra_args = after_args - before_args

        # store extra args onto parser so we can get to it in self.build()
        setattr(parser, "_rezbuild_extra_args", list(extra_args))