Changed NewScheduler function signature

Added or corrected minor changes to documentation
Fixed timePlanner to only return the planned time once

timePlanner was not correctly returning NoMore after the first call
to PlanJob. This due to having no promise in-place that PlanJob will
only be called once per pre-execution calculations.
Added FuncJob tests
Fixed wrong channel usage in Scheduler.Stop

Fixed missing sortedQueue allocation in NewScheduler

Added tests for above cases and one for general task execution,
the latter is an unreliable test that needs to be looked over
again.
Made TestSchedulerDelay be delta based rather than pure sleeps.

This returns the test times back to manageable length