Return a new ``<Relationship>`` element.

def new(cls, rId, reltype, target, target_mode=RTM.INTERNAL):
        """
        Return a new ``<Relationship>`` element.
        """
        xml = '<Relationship xmlns="%s"/>' % nsmap['pr']
        relationship = parse_xml(xml)
        relationship.rId = rId
        relationship.reltype = reltype
        relationship.target_ref = target
        relationship.targetMode = target_mode
        return relationship