Consider having a wrapper to make any Promise cancelable

[tkrugg]

API suggestion

let promise = new Promise(...)
promise = CancelablePromise.from(promise);
promise.cancel();

[mattberkowitz]

let promise = new Promise(...)
promise = CancelablePromise.resolve(promise);
promise.cancel();

should do what you want. See https://codesandbox.io/s/ox1lw5908y

[tkrugg]

@mattberkowitz sounds good!