message: docs(using): document the operator
  Document 'using' operator, describing what
  it accepts and returns. Describe how resulting
  Observable will behave and when unsubscribe
  method from resource object will be called.
diff: @@ -10,7 +10,37 @@ import { OuterSubscriber } from '../OuterSubscriber';
  * @hide true
  */
  export class UsingObservable<T> extends Observable<T> {
  -
  + /**
  + * Creates an Observable that uses a resource which will be disposed at the same time as the Observable.
  + *
  + * <span class="informal">Use it when you catch yourself cleaning up after an Observable.</span>
  + *
  + * `using` is a factory operator, which accepts two functions. First function returns a disposable resource.
  + * It can be an arbitrary object that implements `unsubscribe` method. Second function will be injected with
  + * that object and should return an Observable. That Observable can use resource object during its execution.
  + * Both functions passed to `using` will be called every time someone subscribes - neither an Observable nor
  + * resource object will be shared in any way between subscriptions.
  + *
  + * When Observable returned by `using` is subscribed, Observable returned from the second function will be subscribed
  + * as well. All its notifications (nexted values, completion and error events) will be emitted unchanged by the output
  + * Observable. If however someone unsubscribes from the Observable or source Observable completes or errors by itself,
  + * the `unsubscribe` method on resource object will be called. This can be used to do any necessary clean up, which
  + * otherwise would have to be handled by hand. Note that complete or error notifications are not emitted when someone
  + * cancels subscription to an Observable via `unsubscribe`, so `using` can be used as a hook, allowing you to make
  + * sure that all resources which need to exist during an Observable execution will be disposed at appropriate time.
  + *
  + * @see {@link defer}
  + *
  + * @param {function(): ISubscription} resourceFactory A function which creates any resource object
  + * that implements `unsubscribe` method.
  + * @param {function(resource: ISubscription): Observable<T>} observableFactory A function which
  + * creates an Observable, that can use injected resource object.
  + * @return {Observable<T>} An Observable that behaves the same as Observable returned by `observableFactory`, but
  + * which - when completed, errored or unsubscribed - will also call `unsubscribe` on created resource object.
  + * @static true
  + * @name using
  + * @owner Observable
  + */
  static create<T>(resourceFactory: () => AnonymousSubscription | void,
  observableFactory: (resource: AnonymousSubscription) => SubscribableOrPromise<T> | void): Observable<T> {
  return new UsingObservable<T>(resourceFactory, observableFactory);
  