Typed async events

[mmkal]

This switches from nodejs's EventEmitter to emittery for a few reasons:

• type-safe events. This will prevent people doing things like .on('migration', ...) instead of .on('migrating', ...) etc. It also types the event payload - especially important now since the payload is changing slightly
• async events. this.emit(...) now returns a promise, which we can await. Which means in a follow-up, we can add beforeAll and afterAll events, which will enable use cases like locking the migration table. That wouldn't be possible with sync events.
• apparently, less chance of memory leaks 🤷

The API is smaller than EventEmitter which makes this a breaking change by itself. emittery only supports single payloads too, meaning we can no longer emit('migrating', m.name, m) - but that was pretty redundant anyway, so it makes sense to update to MigrationParams as part of the major (v3) release.

[mmkal]

@papb keeping the merge train going, but again feel free to comment! 🚂

[papb]

Great!

[papb]

Why did you decide to move from ^ to ~ in our dependencies?

[mmkal]

I think tilde is the default for renovate, although I could be wrong because they call out that in most cases you won't get fixes if you use it: https://docs.renovatebot.com/dependency-pinning/#tilde-vs-caret. Happy to re-visit.

[papb]

Yeah, I believe caret is better.