title: pandas: plot histogram with time on x axis
body: <p>I have a Dataframe <code>df</code> like that:</p>
  
  <pre><code>Datetime                 Dollar
  
  2009-08-01 00:00:00        87
  
  2009-08-01 00:15:00        32 
  
  2009-08-01 00:30:00        19 
  
  2009-08-01 00:45:00       128
  </code></pre>
  
  <p>If I try <code>df.hist()</code>, I only get the values (ascending) on the <code>x</code> axis and the specific quantity on the <code>y</code> axis. But I need the timestamp on the <code>x</code> axis for analyzing the changes in value over the time.</p>