code: protected <E extends Event> Listener subscribeEvent(Class<E> eventClass, final Class<? extends Listener<E>> listenerClass) {
          Listener<E> listener = locator.createAndInitialize(listenerClass);
          subscribe(eventClass, listener);
          return listener;
      }
docs: <p>subscribeEvent.</p>
  
  @param eventClass    a {@link java.lang.Class} object.
  @param listenerClass a {@link java.lang.Class} object.
  @return a {@link ameba.event.Listener} object.
  @since 0.1.6e
  @param <E> a E object.