kotlin coroutines and akka actors

These are some experiments in what suspendable functions and channels can mean for Akka.
I wrote an article about it.

• use channels to send messages to an Akka actor and receive them.
• a channel as inbox in the actor implementation. Calling async methods as suspending functions.
• a channel as inbox in the actor implementation with exception handling.

Also in there:

• use suspendable functions to call (ask) akka actor.
• use functions with receiver for an imperative seeming api.
• use extension functions to document the request response protocol for the actor.
• make actorsystem available in coroutine context.
• make akka actor be the coroutine context so it can call suspendable functions. The coroutines involved have the lifecycle of the actor.

Kotlin actors send a CompletableDeferred in a message to an actor. We can do this for Akka. But that won't work across a cluster of course. So it's of limited use.