(chore) clean up CSS classes reference docs (#2714)
(chore) clean up CSS classes reference docs (#2714)

Clarify use of CSS classes a bit more.

- Make it clear the ReasonML classes are not for use.
- Add `operator` and `punctuation`
- Clarify `type` and a few others...
carlokok/highlight.js,carlokok/highlight.js,highlightjs/highlight.js,carlokok/highlight.js,highlightjs/highlight.js,highlightjs/highlight.js,isagalaev/highlight.js,carlokok/highlight.js,highlightjs/highlight.js,isagalaev/highlight.js