code: public final static <T, R> Stream<R> flatMapCompletableFuture(final Stream<T> stream,
              final Function<? super T, CompletableFuture<? extends R>> fn) {
          return stream.flatMap(in -> Streams.completableFutureToStream(fn.apply(in)));
  
      }
docs: <pre>
  {@code
  assertThat(Streams.flatMapCompletableFuture(Stream.of(1,2,3),
  i->CompletableFuture.completedFuture(i+2))
  .collect(CyclopsCollectors.toList()),
  equalTo(Arrays.asList(3,4,5)));
  
  }
  </pre>