v0.3.0

• Add Promise.requestCancelOnInvalidate(_:) as a convenience for token.requestCancelOnInvalidate(_:).
• Add Promise.requestCancelOnDeinit(_:) as a convenience for adding a token property to an object that invalidates on deinit.
• Better support for OperationQueue with delay/timeout. Instead of using the OperationQueue's underlying queue, we instead use a .userInitiated queue for the timer and hop onto the OperationQueue to resolve the promise.