title: Convert hex string to long
body: <p>Are there any Cocoa classes that will help me convert a hex value in a NSString like <code>0x12FA</code> to a <code>long</code> or <code>NSNumber</code>?  It doesn't look like any of the classes like <code>NSNumberFormatter</code> support hex numbers.</p>
  
  <p>Thanks,
  Hua-Ying</p>