title: Create a new NSError in Swift (to reject a Promise from PromiseKit)
body: <p>I have been trying to use PromiseKit, and I'm stuck at rejecting a promise.</p>
  
  <p>Promise rejection is done either by calling a reject function with an NSError as argument.</p>
  
  <pre><code>func getAPromise() -&gt; Promise&lt;Bool&gt; {
      return Promise&lt;Bool&gt; { fulfiller, rejecter in
          let diceRoll = Int(arc4random_uniform(7))
          if diceRoll &lt; 4 {
               // rejecter(?) how do I call this rejection correctly ?
          } else {
               fulfiller(true)
          }
  }
  </code></pre>
  
  <p>Simply getting an instance of NSError would help me.</p>
  
  <p><strong>EDIT</strong>:</p>
  
  <pre><code>NSError("somedomain", 123, [])
  </code></pre>
  
  <p>complains with "Extra argument in call".</p>