Add ActorOf overload that uses ActorDsl syntax
Merge pull request #458 from HCanber/testkit-actor-dsl

Add ActorOf overload that uses ActorDsl syntax to Testkit:

[Fact]
public void MyTest
{
    var a = ActorOf(c =>
    {
        c.Receive<string>((s, context) => context.Sender.Tell("Hello " + s));
    });
    ...
}