Definition and addition of all arguments.

def add_arguments(self):
        """
        Definition and addition of all arguments.
        """
        if self.parser is None:
            raise TypeError("Parser cannot be None, has create_parser been called?")

        for keys, kwargs in self.args.items():
            if not isinstance(keys, tuple):
                keys = (keys,)
            self.parser.add_argument(*keys, **kwargs)