title: how do I compute a weighted moving average using pandas
body: <p>Using pandas I can compute</p>
  
  <ul>
  <li>simple moving average SMA using <code>pandas.stats.moments.rolling_mean</code></li>
  <li>exponential moving average EMA using <code>pandas.stats.moments.ewma</code></li>
  </ul>
  
  <p>But how do I compute a weighted moving average (WMA) as described in wikipedia <a href="http://en.wikipedia.org/wiki/Exponential_smoothing" rel="noreferrer">http://en.wikipedia.org/wiki/Exponential_smoothing</a> ... using pandas?</p>
  
  <p>Is there a pandas function to compute a WMA?  </p>