code: public static Route.Mapper<Object> rx(final Function<Observable, Observable> observable,
      final Function<Single, Single> single) {
      return rx(observable, single, Function.identity());
    }
docs: Map a rx object like {@link Observable}, {@link Single} or {@link Completable} into a
  {@link Deferred} object.
  
  <pre>{@code
  ...
  import org.jooby.rx.Rx;
  ...
  
  {
  use(new Rx());
  
  with(() -> {
  get("/1", req -> Observable...);
  
  get("/2", req -> Observable...);
  
  ....
  
  get("/N", req -> Observable...);
  
  }).map(Rx.rx(
  observable -> observable.observeOn(Scheduler.io()),
  single -> single.observeOn(Scheduler.io()),
  completable -> completable.observeOn(Scheduler.io())));
  }
  }</pre>
  
  @param observable Observable adapter.
  @param single Single adapter.
  @return A new mapper.