title: How to iterate, by month, between two specified dates
body: <p>I have a website that was launched a few months ago.  I would like to write some code that will look through every month, since launch, and grab metrics for that month.</p>
  
  <p>My question is: What is the best way to specify a start date, and then iterate by month, all the way up until the current month (or to another specified date).</p>
  
  <p>Does anyone have any suggestions?  I'm using PHP and a mySQL database.</p>