title: How to detect if a QString is made up of all numeric characters?
body: <p>What is the best way to tell if a <code>QString</code> is made up of just numbers?</p>
  
  <p>There doesn't appear to be a convenience function in the <code>QString</code> library.</p>
  
  <p>Do I have to iterate over every character, one at a time, or is there a more elegant way that I haven't thought of?</p>