ActorRef specs - An ActorRef should restart when Kill:ed

Complete next missing spec for ActorRef. 

State of the rest of the missing specs:
- **An_ActorRef_should_not_allow_actors_to_be_created_outside_an_ActorOf** - I'm not even sure if this is possible with C# encapsulation.
- **ActoRef binary serialization/deserialization specs** - what is the state of objects binary serialization/deserialization on the present moment? As far as I know, it is present only in Akka.Remote and Akka.Cluster, but how about core Akka project? What are further plans in that matter?