code: public A notificationType(String type) {
          this.headers.add(Pair.of("X-WindowsPhone-Target", type));
          return (A)this;
      }
docs: Sets the type of the push notification being sent.
  
  As of Windows Phone OS 7.0, the supported types are:
  <ul>
  <li>token (for Tile messages)</li>
  <li>toast</li>
  <li>raw</li>
  </ul>
  
  This method should probably not be called directly, as the concrete
  builder class will set the appropriate notification type.
  
  @param type  the notification type
  @return  this