Cats Effect: STM & TRef

[jdegoes]

Introduce an effect-polymorphic class atop STM and TRef, with a default implementation for any Cats Effect data type (Cats IO, Monix Task, etc.).

package scalaz.zio.interop

trait STM[F[_], +A] {
  ...
}
object STM {
  def succeed[F[_]: ConcurrentEffect, A]: STM[F, A] = ???
  ...
}

trait TRef[F[_], A} { ... }
object TRef { ... }

The methods will all delegate to ZIO STM, but they will take the ZIO effect returned by STM methods and lift it into any effect F[_] that is suitable equipped.

[VladKopanev]

I would like to try this one.

[VladKopanev]

I think for convenience we could add def mapK[G[_]](f: F ~> G): STM[G, A] function to all such classes, not only STM but also Queue, Schedule, Stream & Sink, etc. Because all concurrency primitives from cats-effect has that, I guess we don't wanna users lost such ability. I can do that in same PR (For STM and TRef).

[jdegoes]

@VladKopanev Yes, that would be fantastic!

[ghostdogpr]

Done in #796