code: public EventBus bindAsync(Class<? extends EventObject> eventType, ActEventListener eventListener) {
          return _bind(asyncActEventListeners, eventType, eventListener, 0);
      }
docs: Bind a {@link ActEventListener eventListener} to an event type extended
  from {@link EventObject} asynchronously.
  
  @param eventType
  the target event type - should be a sub class of {@link EventObject}
  @param eventListener
  the listener - an instance of {@link ActEventListener} or it's sub class
  @return this event bus instance
  @see #bind(Class, ActEventListener)