Parse less and scss files

This pull request is for [Simple support for LESS/SCSS](https://trello.com/c/KoK6kPtp/1190-m-simple-support-for-less-scss-in-key-brackets-features).


Well, I think you're right again to generalize this with `indexOf(startChar)`. I was not quite sure about CM tokenizer for other brackets and put this specialized check.