feat(breaking): return errors instead of throwing

[KATT]

Closes #51

Quick PR to showcase #51 (comment)

Hey, I just found this old thread while thinking of adopting emittery.

Would it make sense for emit() to never throw and instead return Promise<null | [unknown, ...unknown]>?

import Emittery from 'emittery';

const emitter = new Emittery<{
  '🦄': string;
}>();

emitter.on('🦄', () => {
  // works
});

emitter.on('🦄', () => {
  throw new Error('💣');
});

const result = await emitter.emit('🦄', 'a');

if (result) {
  // result would be [Error('💣')]
  console.error('Errors', result);
} else {
  console.log('all OK!');
}

[KATT]

An alternative would be to have some sort of global captureUncaughtExceptions setting or whatnot.

Either way, if we'd do this there'd need to be a global handler where you can log failures etc

[KATT]

We decided not to use awaitable event emitters so I will close this, feel free to take the code if it's of interest