title: Encode enum with NSCoding
body: <p>I am implementing NSCoding in my library, but I need to serialize an enum variable and I can't pass it in for the function that takes <code>AnyObject?</code>. How would this be done in Swift? Here is my enum:</p>
  
  <pre><code>enum ServerType {
    case PC
    case PE
  }
  </code></pre>
  
  <p>Also, <code>toRaw()</code> and <code>fromRaw()</code> do not exist for <code>ServerType</code>. The only property I can access is <code>hashValue</code>, and there are no methods I can access.</p>