title: Check if NSNumber is fraction
body: <p>What is the best way of checking if a <code>NSNumber</code> is a fraction?</p>
  
  <pre><code>NumberIsFraction(@(0)); // NO;
  NumberIsFraction(@(0.5)); // YES;
  NumberIsFraction(@(1.0)); // NO;
  </code></pre>
  
  <p>"Best" in terms of border case handling and performance.</p>