Fix highlight references in Markdown fenced code blocks
Fix highlight references in Markdown fenced code blocks

Fixes #1735

We need \K to not interfer with languages own interpretation of ` like multiline strings in javascript

We need \b in e.g. java\b otherwise it blocks javascript

I couldn't get the bare ``` to not block the other highlighters when introducing \K any other way than negative lookahead of all possible highlighers

danr/kakoune,jkonecny12/kakoune,occivink/kakoune,jkonecny12/kakoune,jkonecny12/kakoune,jkonecny12/kakoune,alexherbo2/kakoune,mawww/kakoune,jjthrash/kakoune,occivink/kakoune,casimir/kakoune,lenormf/kakoune,alexherbo2/kakoune,alexherbo2/kakoune,Somasis/kakoune,occivink/kakoune,jjthrash/kakoune,jjthrash/kakoune,Somasis/kakoune,alexherbo2/kakoune,danr/kakoune,lenormf/kakoune,lenormf/kakoune,danr/kakoune,lenormf/kakoune,mawww/kakoune,casimir/kakoune,casimir/kakoune,occivink/kakoune,casimir/kakoune,Somasis/kakoune,danr/kakoune,jjthrash/kakoune,Somasis/kakoune,mawww/kakoune,mawww/kakoune