Effectful filtering of streams operators

[kubukoz]

I often find myself looking for an operator that would allow filtering the stream with an effectful function.

Something like def evalFilter(f: A => F[Boolean]): Stream[F, A], maybe also def evalMapOption[B](f: A => F[Option[B]]): Stream[F, B] (similar to how TraverseFilter's methods look like).

I would like to contribute these, if it looks like a good idea.

[mpilquist]

👍 from me.

[kubukoz]

Done in #1619