title: how to merge cells both column and row wise
body: <pre><code>  sheet.merge_cells 'H3:U3'
    sheet.merge_cells 'H3:H5'
  </code></pre>
  <p>Does not work. First i need to merge columns (H3:U3) then merge it rowwise (H3:H5) to get big rectangle cell. Thanks in advance</p>