title: convert StyleFrame obj to a pandas dataframe after reading a excel file
body: <p>Is it possible to extract pandas dataframe from a styleframe object?</p>
  
  <pre><code>sf = StyleFrame.read_excel("my.xlsx", read_style=True)
  df = sf.to_dataframe()??
  </code></pre>
  
  <p>Panda's read_excel() does not seem to read style from excel so I am thinking of using StyleFrame (which I just found out about), but I need underlying dataframe object so that I can do pure pandas operations on it and use it with other pure dataframes. </p>
  
  <p>Also is it possible to export styleframe object's style to pandas dataframe.style?</p>