code: public static <T> Observable<T> toObservable(final FutureProvider<T> provider) {
      return Observable.create(new FutureProviderToStreamHandler<>(provider));
    }
docs: creates new observable given future provider,
  translating the future results into stream.
  the sequence will be evaluated on subscribe.
  
  @param provider the future provider for translation
  @param <T>      the stream type
  @return the stream