Generate the documentation Makefile.

        Returns:
            (str): the contents of the `Makefile`.

def makefile(self):
        """Generate the documentation Makefile.

        Returns:
            (str): the contents of the `Makefile`.
        """
        return self.env.get_template('Makefile.j2').render(
            metadata=self.metadata,
            package=self.package)