Return a |_Column| object of *width*, newly added rightmost to the
        table.

def add_column(self, width):
        """
        Return a |_Column| object of *width*, newly added rightmost to the
        table.
        """
        tblGrid = self._tbl.tblGrid
        gridCol = tblGrid.add_gridCol()
        gridCol.w = width
        for tr in self._tbl.tr_lst:
            tc = tr.add_tc()
            tc.width = width
        return _Column(gridCol, self)