Convert this cateen information into string
            which is a valid OpenMensa v2 xml feed

            :rtype: str

def toXMLFeed(self):
        """ Convert this cateen information into string
            which is a valid OpenMensa v2 xml feed

            :rtype: str"""
        feed = self.toXML()

        xml_header = '<?xml version="1.0" encoding="UTF-8"?>\n'
        return xml_header + feed.toprettyxml(indent='  ')