Return a |_Row| instance, newly added bottom-most to the table.

def add_row(self):
        """
        Return a |_Row| instance, newly added bottom-most to the table.
        """
        tbl = self._tbl
        tr = tbl.add_tr()
        for gridCol in tbl.tblGrid.gridCol_lst:
            tc = tr.add_tc()
            tc.width = gridCol.w
        return _Row(tr, self)