fixed ThreadLocalVar spec under rbx
Removed incorrectly behaving code I added to fix IVar + Dereferenceable.
removed documentation about Observable
New observers work better with Dereferenceable.

* CopyOnNotifyObserverSet#notify_observers now accepts a block
* CopyOnNotifyObserverSet#notify_and_delete_observers now accepts a block
* CopyOnWriteObserverSet#notify_observers now accepts a block
* CopyOnWriteObserverSet#notify_and_delete_observers now accepts a block
* Agent observer notification uses blocks to better support Dereferenceable
* IVar observer notification uses blocks to better support Dereferenceable
* ScheduledTask observer notification uses blocks to better support Dereferenceable
Future now protects mutation methods inherited from IVar.
some minor style fixes
Improved Supervisor locking policy and small refactorings
Moved object graph image to wiki repo.
Corrected example use of Concurrent::dataflow
Fixed bug in observer sets when block returns complex data types.