title: Combine Date and Time columns using pandas
body: <p>I have a pandas dataframe with the following columns:</p>
  <pre class="lang-py prettyprint-override"><code>data = {'Date': ['01-06-2013', '02-06-2013', '02-06-2013', '02-06-2013', '02-06-2013', '03-06-2013', '03-06-2013', '03-06-2013', '03-06-2013', '04-06-2013'],
          'Time': ['23:00:00', '01:00:00', '21:00:00', '22:00:00', '23:00:00', '01:00:00', '21:00:00', '22:00:00', '23:00:00', '01:00:00']}
  df = pd.DataFrame(data)
  
           Date      Time
  0  01-06-2013  23:00:00
  1  02-06-2013  01:00:00
  2  02-06-2013  21:00:00
  3  02-06-2013  22:00:00
  4  02-06-2013  23:00:00
  5  03-06-2013  01:00:00
  6  03-06-2013  21:00:00
  7  03-06-2013  22:00:00
  8  03-06-2013  23:00:00
  9  04-06-2013  01:00:00
  </code></pre>
  <p>How do I combine data['Date'] &amp; data['Time']  to get the following? Is there a way of doing it using <code>pd.to_datetime</code>?</p>
  <pre><code>Date
  01-06-2013 23:00:00
  02-06-2013 01:00:00
  02-06-2013 21:00:00
  02-06-2013 22:00:00
  02-06-2013 23:00:00
  03-06-2013 01:00:00
  03-06-2013 21:00:00
  03-06-2013 22:00:00
  03-06-2013 23:00:00
  04-06-2013 01:00:00
  </code></pre>