Registers a composer of a format.

        :param type: The unique name of the format
        :param composer: The method to compose data as the format

def register_composer(self, type, composer, **meta):
        """Registers a composer of a format.

        :param type: The unique name of the format
        :param composer: The method to compose data as the format
        """
        try:
            self.registered_formats[type]['composer'] = composer
        except KeyError:
            self.registered_formats[type] = {'composer': composer}
        if meta:
            self.register_meta(type, **meta)