title: Drop specific rows from multiindex Dataframe
body: <p>I have a multi-index dataframe that looks like this:</p>
  
  <pre><code> start      grad
   1995-96    1995-96 15  15  
              1996-97 6   6   
              2002-03 1   1   
              2007-08 1   1   
  </code></pre>
  
  <p>I'd like to drop by the specific values for the first level (level=0). In this case, I'd like to drop everything that has 1995-96 in the first index.</p>