title: Convert pandas DataFrame index to Timestamp format
body: <p>I created a dataframe. Running some commands on the iPython I get the following results:</p>
  
  <pre><code>In [5]: df.tail()
  Out[5]: 
                   open     high      low    close  volume
  date                                                        
  2017-02-22 15:00  1.05131  1.05137  1.05074  1.05075     543
  2017-02-22 15:30  1.05074  1.05165  1.05072  1.05139     506
  2017-02-22 16:00  1.05137  1.05193  1.05121  1.05141     488
  2017-02-22 16:30  1.05144  1.05205  1.05056  1.05065     747
  2017-02-22 17:00  1.05061  1.05167  1.04988  1.04997     753
  
  In [6]: df.index[0]
  Out[6]: '2011-11-21 14:30'
  
  In [7]: type(df.index[0])
  Out[7]: str
  </code></pre>
  
  <p>As you see, the index is in str format but I need it to be in Timestamp format.  Is it possible?</p>