title: Using DateTime to find the amount of months (inclusive) between two dates
body: <p>I have two <code>DateTimes</code>, date1 and date2.</p>
  
  <p>How do I get the difference in months?</p>
  
  <p>2011/01/31 - 2011/02/01 should return 2.<br>
  2011/02/01 - 2011/02/01 should return 1.<br>
  2011/02/01 - 2012/03/01 should return 14.<br>
  etc.</p>