[language support] Javascript

A Javascript documentation runner should be able to be run on Nashorn so that the formatter can be written from Kotlin/JVM. Alternatively, it could be run as a standalone JS app using a Kotlin/JS formatter, bundled into a standalone executable package with something like [@zeit/pkg].(https://github.com/zeit/pkg)

Formatter options:

- Lots of options in this article: https://dev.to/joelnet/lets-talk-about-auto-generated-documentation-tools-for-javascript-49ol