Support event namespace #31

It would be rad if it's possible for creators of libs to create a namespace for their events, it's well used in jQuery for example in Bootstrap.

Bootstrap Modal emit show.bs.modal event, it's allow user to be sure the show event come from the Bootstrap Modal and not an other lib or a general show event.

Currently, except jQuery I don't know an other libs which handle event namespace

See:

• https://api.jquery.com/event.namespace/
• https://getbootstrap.com/docs/4.1/components/modal/#events
• https://github.com/twbs/bootstrap/blob/v4-dev/js/src/modal.js#L47-L51

Note: This issue has a bounty, so it's expected that you are an experienced programmer and that you give it your best effort if you intend to tackle this. Don't forget, if applicable, to add tests, docs (double-check for typos), and update TypeScript definitions. And don't be sloppy. Review your own diff multiple times and try to find ways to improve and simplify your code. Instead of asking too many questions, present solutions. The point of an issue bounty is to reduce my workload, not give me more. Include a 🦄 in your PR description to indicate that you've read this. Thanks for helping out 🙌 - @sindresorhus