Http4s support

[vasiliybondarenko]

It would be nice to support at least http4s beyond current Akka http.

[Odomontois]

I agree.
Moreover, I suppose it's time to define generic formulation, i.e. having the request type as parameter, to have all the F[_] goodness without m * n problem.
Other frameworks (tapir, typedapi, etc.) solve this problem introducing universal request\response types, but I believe it greatly limits use of existing solutions for akka-http\http4s\finagle in the middleware and atom implementations.
So the best thing now would be introducing

trait Routed[F[_], Req]

trait HttpRequest[Req]

to build a unified model for all major Http implementations

[REDNBLACK]

WIP #479