Safer initialization of the Async internal synchronization objects.
Merge pull request #95 from jdantonio/fix/async-initialization

Safer initialization of the Async internal synchronization objects.
Removed C extension file erroneously added during experimental development.
Added Larry Lv to contributor list in README.
Updated README.
Fixed Yard errors.
Renamed mutex instance variable in Async to avoid naming collisions.
Another brittle supervisor test.
Moved all custom errors into a single file and into the Concurrent module.
Returned AbortError to TVar.
Merge pull request #96 from jdantonio/refactor/errors

Moved all custom errors into a single file and into the Concurrent module
Raw port of Actress

needs more work and discussions
Change Abstract actor class to a ActorContext module
Remove Algebrick dependency
when spawn returns children are set
Reject all envelops sent to termiated actor before actor is GCed
Remove dead code
Remove dependency on Atomic
Remove unused mutex

no instance variables are being reassigned
Add Reference#ask!