code: public final static <T, R> Stream<R> concatMapterable(final Stream<T> stream, final Function<? super T, ? extends Iterable<? extends R>> fn) {
          return stream.flatMap(fn.andThen(c -> stream(c)));
  
      }
docs: flatMap operation that allows a Collection to be returned
  <pre>
  {@code
  assertThat(Streams.flatMapCollection(Stream.of(20),i->Arrays.asList(1,2,i))
  .collect(CyclopsCollectors.toList()),
  equalTo(Arrays.asList(1,2,20)));
  
  }
  </pre>