let's say you have more than one future:

    findAirline:        AirlineCode =>                Future[Option[Airline]]
    getFlightsForToday: Airline =>                    Future[Seq[Flight]]
    findAvailable:      Seq[Flight] => Constraints => Future[Option[Flight]

compose them so that I get:

    findFlight: AirlineCode => Constraints => Future[Flight]

I don't want `Future[Option[Flight]]` since Future has own error handling (using Try). No cheating by using scalaz monad transformer.