code: public static FuncN<Observable<Void>> toAsync(final ActionN action, final Scheduler scheduler) {
          return toAsync(Actions.toFunc(action), scheduler);
      }
docs: Convert a synchronous action call into an asynchronous function call through an Observable.
  <p>
  <img width="640" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/toAsync.ans.png" alt="">
  
  @param action the action to convert
  @param scheduler the Scheduler used to execute the {@code action}
  @return a function that returns an Observable that executes the {@code action} and emits {@code null}
  @see <a href="https://github.com/ReactiveX/RxJava/wiki/Async-Operators#wiki-toasync-or-asyncaction-or-asyncfunc">RxJava Wiki: toAsync()</a>