code: public <R> ReactiveSeq<R> mergeMap(final int maxConcurrency, final Function<? super T, ? extends Publisher<? extends R>> mapper) {
          return Spouts.fromIterable(this).mergeMap(maxConcurrency,mapper);
      }
docs: A potentially asynchronous flatMap operation where data from each publisher may arrive out of order
  
  @param mapper
  @return