title: pandas: combine two index columns
body: <p>I have the following pandas Series:</p>
  
  <pre><code>data = {(pd.Timestamp('2016-01-01 00:00:00'), datetime.time(0, 0)): 6.885,
          (pd.Timestamp('2016-01-01 00:00:00'), datetime.time(0, 5)): 6.363, 
          (pd.Timestamp('2016-01-01 00:00:00'), datetime.time(0, 10)): 6.093,
          (pd.Timestamp('2016-01-01 00:00:00'), datetime.time(0, 15)): 6.768, 
          (pd.Timestamp('2016-01-01 00:00:00'), datetime.time(0, 20)): 7.11}
  s = pd.Series(data)
  
  2016-01-01  00:00:00    6.885
              00:05:00    6.363
              00:10:00    6.093
              00:15:00    6.768
              00:20:00    7.110
  dtype: float64
  </code></pre>
  
  <p>How can I combine the two index columns to create a <code>DatetimeIndex</code> like so:</p>
  
  <pre><code>2016-01-01 00:00:00    6.885
  2016-01-01 00:05:00    6.363
  2016-01-01 00:10:00    6.093
  2016-01-01 00:15:00    6.768
  2016-01-01 00:20:00    7.110
  dtype: float64
  </code></pre>