highlight-js support

[Devasta]

Merry Christmas, all!

Just FYI, I've made a start on building support for highlight.js and hope to complete sometime in the new year, as its used by Stackoverflow and Discord.

There is zero chance of them adding to the core as they have stopped accepting new languages, but will be good to have anyway.

There is just one issue... my regex is as bad as my JS! I'm learning both as I go, so if anyone is able to help with it that'd be appreciated. :)

https://github.com/Devasta/highlightjs-kdl

Hope Santa has lots of presents for ye!

Regards

Dan