Implemented the ability to subscribe to the main thread from the base class twice or more times.

Author: swedesjs

lib/src/vkdart/fetch/abstract_update_fetcher.dart

@@ -7,7 +7,7 @@ abstract class AbstractUpdateFetcher {
   final StreamController<VkDartUpdate> _updatesController;
 
   /// constructor
-  AbstractUpdateFetcher() : _updatesController = StreamController();
+  AbstractUpdateFetcher() : _updatesController = StreamController.broadcast();
 
   /// add [update] to updates stream.
   void emitUpdate(VkDartUpdate update) => _updatesController.add(update);

lib/src/vkdart/vkdart.dart

@@ -86,13 +86,16 @@ class VkDart extends Vkontakte {
 
   /// Start fetcher
   Future<void> start() async {
-    fetcher.onUpdate().listen(_event.emitUpdate);
+    onUpdate().listen(_event.emitUpdate);
     return fetcher.start();
   }
 
   /// Stop fetcher
   Future<void> stop() => fetcher.stop();
 
+  /// Listen for events.
+  Stream<VkDartUpdate> onUpdate() => fetcher.onUpdate();
+
   /// Listen for `message_new`, `message_edit`, `message_reply` events.
   Stream<VkDartMessageUpdate> onMessage() =>
       _event.onMessage().map((event) => VkDartMessageUpdate(this, event));