feat: convert project to typescript

[robertsLando]

@mcollina would you accept such PR?

[mcollina]

Why? What's the end goal? This project is stable and essentially "done".

[robertsLando]

From my experience re-writing projects using TS helps discover issues in the code that JS hides, also it's easier to apply any future update to the library giving that everything is type-safe then.

Also having to deal with #151 (comment) would make things easier to handle

[mcollina]

Unless some significant feature is coming (like a new version of MQTT), it's not worth doing it.

Usually, it's harder to get typescript code to be as fast as JS, and a rewrite would require extensive benchmarks.

I'm not necessarily opposed, but given the amount of work needed on on MQTT.js, I don't think it's a good use of effort.

It might make sense doing it if we end up adding some support for the WHATWG specs.