title: Convert pivot tables to dataframe
body: <p>I have a pivot table, for example,</p>
  
  <pre><code>first second                    
  bar   one  
        two    
  foo   one  
        two 
  </code></pre>
  
  <p>How do I change it back to a normal dataframe with all values and rows and column filled?</p>
  
  <pre><code>first second                    
  bar   one 
  bar   two  
  foo   one 
  bar   two
  </code></pre>