title: Sort dataframe by string length
body: <p>I want to sort by name length. There doesn't appear to be a <code>key</code> parameter for <code>sort_values</code> so I'm not sure how to accomplish this. Here is a test df:</p>
  
  <pre><code>import pandas as pd
  df = pd.DataFrame({'name': ['Steve', 'Al', 'Markus', 'Greg'], 'score': [2, 4, 2, 3]})
  </code></pre>