title: Filter out rows/columns with zero values in MultiIndex dataframe
body: <p>I have the following panda MultiIndex dataframe in python </p>
  
  <pre><code>             0         1         2         3 
  bar one  0.000000 -0.929631  0.688818 -1.264180
      two  1.130977  0.063277  0.161366  0.598538
  baz one  1.420532  0.052530 -0.701400  0.678847
      two -1.197097  0.314381  0.269551  1.115699
  foo one -0.077463  0.437145 -0.202377  0.260864
      two -0.815926 -0.508988 -1.238619  0.899013
  qux one -0.347863 -0.999990 -1.428958 -1.488556
      two  1.218567 -0.593987  0.099003  0.800736
  </code></pre>
  
  <p>My questions, how can I filter out:</p>
  
  <ol>
  <li>Columns that contains zero values -- column 0, in the above example.</li>
  <li><p>With regrade to rows filtering. How can I filter rows with zeros: (bar, one) alone and how can I filter both (bar, one) and (bar, two)?</p>
  
  <p>(Apologies for my not native English ;)</p></li>
  </ol>