def emit(type, sender=nil, *args)
      listeners[type].each { |l| l.fire(sender, *args) } if listeners.has_key? type
    end
def emit(type, sender=nil, *args)
      listeners[type].each { |l| l.fire(sender, *args) } if listeners.has_key? type
    end
Emit an event of type +type+ and call all the registered listeners to this event.
 The +sender+ param will help the listener to identify who is emitting the event.
 You can pass then every additional arguments you'll need