title: How to get the difference between two QDateTimes in milliseconds?
body: <p>I wish QDateTime overrode the - operator and returned a QTimeSpan representing the difference between two QDateTimes (just like .NET's TimeSpan). Since this doesn't exist in Qt, I decided to implement it.</p>
  
  <p>Unfortunately, QDateTime has no <code>msecsTo</code>-like function. What is the cleanest way to get the difference between two QDateTimes accurate to the millisecond?</p>