ESM packaging

Hi, would it be possible to offer ESM-friendly packaging for frameworks wishing to support _hyperscript?

The goal is to be able to pass the build system something like
`export { default } from "hyperscript.org";`

Or with advanced features,

`export { default, workers, socket, eventsource } from "hyperscript.org";`

such that the build system can bundle it in into one file, and hyperscript's side-effecting the DOM can still work.

It would typically involve using the `exports` field in `package.json`.