Changed ProviderInterface for clarity:
 * Split release() into commit() and rollback()
 * Refactored to allow for 'skippable' logic to take place in the scheduler.

Changed schedules and events:
 * Schedules no longer need to hold job/task information
 * Events mush now provide an Icecave\Skew\Entities\TaskDetailsInterface

The scheduler itself has not yet been updated.