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