[Feature] Promise-based API?

[dominique-mueller]

Right now, cpx can be used either synchronously, or asynchronously using callbacks. With the trend in the world of NodeJS to move to native Promises - what about providing a promise-based API?

Perhaps something like copyAsync? Or replacing the copy and introducing a breaking change?

[cypherix93]

This would be a great addition, especially with async/await being the norm these days.

This probably wouldn't need a breaking change since you can just drop the last callback parameter in copy and it will treat it as if a Promise is expected.

[MickL]

Would be awesome to prevent a callback-hell!
Personally I would prefer to additionally to copy that returns a promise to have copySync, too.