Updated CancellationTokenSourceExtensions to properly handle multiple calls to CancelAfter, and not prevent GC from reclaiming a CancellationTokenSource which is pending cancellation.
Relax timing tolerance to improve test success percentage without substantially impacting the interpretation of results
Add tests for proper argument validation in CoreTaskExtensions
Relax timing constraints in TestCompletedTask
Add test for null passed to CompletedTask.FromResult
Merge pull request #18 from sharwell/completed-tasks

Completed tasks testing
Merge pull request #17 from sharwell/argument-validation

Add tests for proper argument validation in CoreTaskExtensions
Merge pull request #16 from sharwell/cancellation-behavior

Cancellation behavior