Rework Promises implementation to be Promises/A+ compliant.

[johnyanarella]

This work is already underway in the promises_aplus branch.

[johnyanarella]

Promises A+ specification

Promises A+ compliance suite

[johnyanarella]

Issues #41 and #74 are already resolved in this new branch, as well.

[johnyanarella]

NOTE: This commit includes breaking API changes.

Rewrote Deft JS's Promise and Deferred implementations to be Promises/A+ compliant:

• onFulfilled and onRejected handlers are now guaranteed to be called in a future turn of the event loop (eliminating an entire class of runtime errors in applications that did not anticipate that these handlers were sometimes called immediately).
• Rewrote cancellation as a rejection with a CancellationError.
• Rewrote progress handler registration and propagation logic to support progress value transformation.
• Eliminated Deferred and Promise API redundancies
  • ex. deferred.then() is now accomplished via deferred.promise.then()
• Deft JS's Promises now pass the Promises/A+ Test Suite v1.3.1.

The new implementation is covered by 711 unit tests and will be the API that will be maintained as we move forward to version 1.0.

See also: #83, #84, #61, #74 and #41.