feat/event-listeners

[mohitpubnub]

feat: support for new event listeners

example syntax:

 //adhoc event specific listener:
Channel firstChannel = pubnub.Channel("first");
var subscription = firstChannel.Subscription();
subscription.OnMessage = (Pubnub pn, PNMessageResult<object> messageEvent) => {
	Console.WriteLine($"Message received {messageEvent.Message}");
};
subscription.Subscribe<object>();

// OR general syntax for event listener with entities
SubscribeCallbackExt eventListener = new SubscribeCallbackExt(
	delegate (Pubnub pn, PNMessageResult<object> messageEvent) {
		Console.WriteLine($"received message {messageEvent.Message}");
	},
	delegate (Pubnub pn, PNPresenceEventResult e) {

		Console.WriteLine("Presence event");
	}
);
Channel firstChannel = pubnub.Channel("first");
var subscription = firstChannel.Subscription(SubscriptionOptions.ReceivePresenceEvents);
subscription.AddListener(eventListener);
subscription.Subscribe<object>();

// Similar code for ChannelGroup and SubscriptionSet