first pass as docs for what regex features we support
first pass as docs for what regex features we support

MakeNowJust/highlight.js,MakeNowJust/highlight.js,highlightjs/highlight.js,palmin/highlight.js,palmin/highlight.js,highlightjs/highlight.js,highlightjs/highlight.js,carlokok/highlight.js,MakeNowJust/highlight.js,carlokok/highlight.js,palmin/highlight.js,carlokok/highlight.js,isagalaev/highlight.js,carlokok/highlight.js,highlightjs/highlight.js,isagalaev/highlight.js