title: increment date by one month
body: <p>Let's say I have a date in the following format: 2010-12-11 (year-mon-day)</p>
  
  <p>With PHP, I want to increment the date by one month, and I want the year to be automatically incremented, if necessary (i.e. incrementing from December 2012 to January 2013).</p>
  
  <p>Regards.</p>