title: Set width and height of an image when inserting via worksheet.insert_image
body: <p>From the <a href="http://xlsxwriter.readthedocs.org/worksheet.html#insert_image" rel="noreferrer">docs</a>, the <code>insert_image</code> function takes the following options:</p>
  
  <pre><code>{
      'x_offset':    0,
      'y_offset':    0,
      'x_scale':     1,
      'y_scale':     1,
      'url':         None,
      'tip':         None,
      'image_data':  None,
      'positioning': None,
  }
  </code></pre>
  
  <p>The problem is that the size of input images I need to insert can vary, but the cell where they need to be is of a fixed size. Is it possible to somehow provide a width and a height and let Excel resize the image into the provided dimensions?</p>