title: pandas rolling window mean in the future
body: <p>I would like to use the <a href="https://pandas.pydata.org/pandas-docs/version/0.22/generated/pandas.DataFrame.rolling.html" rel="nofollow noreferrer"><code>pandas.DataFrame.rolling</code></a> method on a data frame with datetime to aggregate future values.
  It looks it can be done only in the past, is it correct?</p>