def use_two_cell_anchor
      return if @anchor.is_a?(TwoCellAnchor)
      new_anchor = TwoCellAnchor.new(@anchor.drawing, :start_at => [@anchor.from.col, @anchor.from.row])
      swap_anchor(new_anchor)
    end
def use_two_cell_anchor
      return if @anchor.is_a?(TwoCellAnchor)
      new_anchor = TwoCellAnchor.new(@anchor.drawing, :start_at => [@anchor.from.col, @anchor.from.row])
      swap_anchor(new_anchor)
    end
changes the anchor type to a two cell anchor