title: How to freeze entire header row in openpyxl?
body: <p>How to freeze entire header row in openpyxl? 
  So far I can only freeze the column:</p>
  
  <pre><code># only freeze the column (freeze vertically)
  cell = ws.cell('{}{}'.format(col, row_idx+1))  
  worksheet.freeze_panes = cell
  </code></pre>