Implementing Notification Callbacks

Implement the notification callback by getting the PTNotification from the NSNotification user info, and reading its values by using the key PTMediaPlayerNotificationKey:

- (void) onMediaPlayerNotification:(NSNotification *) nsnotification {
    PTNotification *notification = [nsnotification.userInfo objectForKey:PTMediaPlayerNotificationKey];
    NSLog(@"Notification: %@", notification);
}