[Proposal] Refactor the entire code base to Promise-based

[SukkaW]

We can use async and await to organize the codebase and universalify.fromPromise to create Node.js-callback style APIs from the promise-based APIs.

[RyanZim]

Yeah; that'd be great. It's a ton of work, but if you want to take a stab at it, you're more than welcome to! Just please make granular PRs; not one gigantic PR that takes hours to review.

[SukkaW]

Yeah; that'd be great. It's a ton of work, but if you want to take a stab at it, you're more than welcome to! Just please make granular PRs; not one gigantic PR that takes hours to review.

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Sure! Let's do one API migration per PR. And I can make each PR safe to even be included in a minor version bump (a.k.a. No breaking changes!).

I will list the roadmap here for progress tracking:

• [x] copy: #1021
• [x] empty: The emptyDir's implementation is already Promise-based, see #885
• [x] ensure: https://github.com/jprichardson/node-fs-extra/pull/1023
• [x] json: The json is just a re-export of jsonfile module
• [x] mkdirs: The mkdirs's implementation is already Promise-based
• [x] move: https://github.com/jprichardson/node-fs-extra/pull/1025
• [x] output-file: https://github.com/jprichardson/node-fs-extra/pull/1024
• [x] path-exists: The pathExists's implementation is already Promise-based
• [x] remove: The remove is just a simple wrapper of graceful-fs#rm, no need to refactor

[RyanZim]

Closing as this is now completed. Thanks again for all your efforts here!