Refactored TimerTask specs.
Merge pull request #75 from jdantonio/refactor/timer-task-specs

Refactored TimerTask specs.
Prerelease 0.6.0.pre.2
Fixed brittle RubyThreadPoolExecutor spec.
IVar: move MultipleAssignmentError into the class.
IVar: documentation.
MVar: documentation.
TVar: documentation.
IVar: fix example markup.
Mutex version of atomic reference.
Changed every mutex.lock - mutex.unlock pair to ensure mutex release even with errors
closes #79
Add 4 convenience methods to obligation

wait - waits and returns self
no_error! - waits and raises on rejection, otherwise returns self
value! - returns value, or raises if rejected
exception - allows to call `raise rejected_ivar`
Add Observable#with_observer returning self
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