add lazy register for actors
Moving lazy register under Concurrent adding docs
Fix Context logging
Adding dead letter routing
Allow to set custom Reference class
Fix broken Delay#value!

Use global_task_executor to perform the task be default. Use
immediate executor in configuration related Delays before
global_task_executor is up an running.
Add missing dependency of Future on IVar
Break up actor core into series of behaviors

add message redirecting
Add ability to link Actors

actor will get notified when linked actor fails
Rename Actress to Actor

keep Actress around for compatibility
Add Context#default_reference_class

to able to easily override default reference class
Update doc
Pass the envelope explicitly next in Context if not recognized
Remove Context#spawn

Actor.spawn or AnActor.spawn should be used instead as
it depends on global Actor.current. It's also more similar to
Kernel.spawn.
Do not silently ignore :class option in AContext.spawn
Add await behavior
Doc update
Buffer optimization

if nothing is scheduled execute the message right away do not pass
it to another scheduling block, saves context switching
Add atomic linking

`AnActor.spawn name: 'an', link: true` will be linked before any
message is received.
Do not create un-GC-able symbols when creating ThreadLocalVars

GC all data for a given thread local var when the var is GCed