title: how to specify the datetime format in read_csv
body: <p>I have a file where each row has this format:</p>
  
  <pre><code>YYYY-MM-DD-HH-MM-SS  uint64 float64 float64 uint64
  </code></pre>
  
  <p>I've read it with:</p>
  
  <pre><code>pd.read_csv('file.txt', sep=' ', header=None, index_col=0, names= ('C1', 'C2', 'C3', 'C4'), use_unsigned=True, parse_dates=True, infer_datetime_format=True)
  </code></pre>
  
  <p>The datetimes constructed are not correct.
  Can I specify the exact format?</p>