Remove Obligation from Future.

Because Future inherits from IVar, which already includes Obligation.
Merge pull request #93 from larrylv/remove-obligation-from-future

Remove Obligation from Future.
Add Delay#reconfigure method

allows to replace the block evaluating to the value with new one
only if a delay is still incomplete?
Fix configuration to be thread safe

by replacing ||= operator with Delay instances
remove unsafe mutex from configuration
Fix processor count

use Delay same as in configuration
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!
TODOs and comments update
Split files and add documentation
Add Actress::AdHoc actor

it's behavior is given by proc passed on initialization
Configurable Core

executor can be configured, other options will follow
spawn can be also called with hash instead of class, name, *args