Add AwaitStore

src/observable.ts

@@ -43,6 +43,8 @@ export default class Observable<T = any> {
       let oldcb = this.subscriber.find(e => e === callback);
       if (!oldcb)
          this.subscriber.push(callback)
+
+      return () => this.unsubscribe(callback);
    }
 
    unsubscribe(callback: ObserverCallback<T> | ObserverCallbackCollect<T>) {