Backport promise cancellation support to v1 Promise API#48

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jsor merged 6 commits intoreactphp:1.0from

clue-labs:cancellable

Feb 27, 2016

Commits on Feb 26, 2016

Cancellation handler must only be called once
clue
committed

Commits on Feb 27, 2016

Throw InvalidArgumentException for invalid canceller
clue
committed