code: public static Function<? super ReactiveSeq<Long>, ? extends ReactiveSeq<Long>> flatMapLongs(LongFunction<? extends LongStream> b){
  
          return a->a.longs(i->i,s->s.flatMap(b));
      }
docs: /*
  Fluent flatMap operation using primitive types
  e.g.
  <pre>
  {@code
  import static cyclops.ReactiveSeq.flatMapLongs;
  
  ReactiveSeq.ofLongs(1,2,3)
  .to(flatMapLongs(i->LongStream.of(i*2)));
  
  //[2l,4l,6l]
  }
  </pre>