Fix various typos in the README

Add PromiseOperation class

Mark TWLBlockOperation as ready if it gets cancelled

Rebuild docs

Rebuild docs

Bump version to v1.4.0

Remove hard line wrapping from the README

Add Promise.makeChild()

Document that tap().requestCancel() does nothing

Change cancellation propagation behavior of onCancel

Fix cancellation propagation of resolve(with:) and flatMap

Enhance Obj-C test helpers for expectations

Update .mailmap

Fix unnecessarily mutable local variable

Implement the stack usage optimization for Obj-C too