When publishing these packages, publish built / transpiled JavaScript

Cool project!

@achingbrain When publishing these packages to npm, etc., would you consider publishing built / transpiled JavaScript using a tool like [rollup](https://github.com/rollup/rollup)? Otherwise it makes it hard to use these libs in a project with a different Babel config.

This would mean adding a build script for each child package so that they're all run with the lerna command from the root dir.

Thanks!