Add Free.liftF - lifts a value from within a Functor into Free

    scala> scalaz.Free.liftF(Some(1): Option[Int])
    res1: scalaz.Free[Option,Int] = Suspend(Some(Return(1)))
Merge pull request #618 from puffnfresh/free-liftf

Add Free.liftF - lifts a value from within a Functor into Free