feat: always return a promise from the stopper function

[SimenB]

As mentioned in #295, the return value of the stopper function seems inconsistent. This makes it always return Promise<null> regardless of when it's called.

An open question is - does Native.stop resolve with a value? I tested locally and it always resolved to undefined, so I'm thinking just resolving to null is fine. But I don't know C, so it might resolve to something else in some cases?

(I've also updated the readme with the new event from #286).

[paulmillr]

I don't think this would work correctly. Recalling a case when I was editing some code and decided to do the same change. fsevents broke after it.

But I may be wrong. Did you test it on something?

[SimenB]

But I may be wrong. Did you test it on something?

I just tested it locally, not especially thoroughly. I didn't actually know about the stop function until looking into it today 😬 Unsure why it would break anything though?

[paulmillr]

There is some asynchronous code that may be getting called at some point. It’s all messy and related to race conditions - for example, when fsevents instances got closed already. Not really easy to test!