Implicit def for more comlex HLists of futures

hconsIsHListOfFutures.scala

implicit def hconsIsHListOfFutures[H, In <: HList, Out <: HList]
     (implicit ev: IsHListOfFutures[In, Out]): IsHListOfFutures[Future[H] :: In, H :: Out] = new IsHListOfFutures[Future[H] :: In, H :: Out] {

  override def hsequence(l : Future[H] :: In)(implicit ec: ExecutionContext): Future[H :: Out] = {
    val head = l.head
    val tail = l.tail
    head.flatMap(h => ev.hsequence(tail).map(h :: _))
  }
}