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

def new(rId, reltype, target, target_mode=RTM.INTERNAL):
        """
        Return a new ``<Relationship>`` element.
        """
        xml = '<Relationship xmlns="%s"/>' % nsmap['pr']
        relationship = parse_xml(xml)
        relationship.set('Id', rId)
        relationship.set('Type', reltype)
        relationship.set('Target', target)
        if target_mode == RTM.EXTERNAL:
            relationship.set('TargetMode', RTM.EXTERNAL)
        return relationship