Abort support

[jack-sf]

Have you thought about adding support also for aborting the reqeusts? ( https://developer.mozilla.org/en-US/docs/Web/API/AbortController/abort )

On browser environment, we could use have a ponyfill similar to this polyfill: https://github.com/mo/abortcontroller-polyfill .

On node environment, node-fetch seems to already support AbortController: node-fetch/node-fetch#95 .

So this fetch-ponyfill could also ponyfill the abortcontroller, and export AbortController and AbortSignal. WDYT?

[qubyte]

I see no need. It looks like abortcontroller-polyfill is already usable as a ponyfill already, and when node-fetch supports abort, it'll get into this library naturally as dependencies are updated.