Use implicit ActorRefFactory instead of ActorSystem for creating SlackRTMClient

[vavison]

The creation of a SlackRTMClient requires an implicit ActorSession to be in scope

object SlackRtmClient {
  def apply(token: String, duration: FiniteDuration = 5.seconds)(implicit arf: ActorSystem): SlackRtmClient = {
    new SlackRtmClient(token, duration)
  }
}

I'm quite new to Akka so may have misunderstood something, but I think that this means all of the ActorRefs created by the SlackRtmClient will sit at the top level of the actor hierarchy?

Ideally, I would like these to be able to sit underneath other actors in the actor hierarchy. I think this would be possible by changing the implicit ActorSystem to be an implicit ActorRefFactory so that we can use the actor context instead of the system. I couldn't see anywhere where it needed to explicitly be an ActorSystem but there's a good chance I missed something!

I'm happy to work on this if you think it's a good idea. Please let me know if I've missed an important point somewhere.

[mccartney]

(another contributor here)

While I understand what you mean, I don't know enough of Akka to have some say.
I suggest you create a PR. I'll review it - either myself or consult with someone more knowledgeable with Akka.

Thanks.