rework the documentation

[pmlopes]

upstream vertx is reworking the documentation to focus only on java, kotlin. As we are polyglot developers, instead of duplicating the documentation on es4x site with half broken machine translated code, I think we should have independent documentation and point upstream for the details.

A user that can read javascript can also read to some extent java code and vice versa. As the examples in the docs are simple enough, I don't see this as a problem.

On es4x side, we should have documentation as an example, and for the explanations of the details links.