Add highlighting of one line comments

I really often thinking in comments and adding it in form of `// my thoughts`

It will be very useful to add it

P.S. need to think about the links!

Start by locating the IntelliJ IDEA syntax-highlighting implementation for xit files and compare how existing syntax elements are handled. Clarify the unresolved question about links before implementation; done means `// my thoughts` comments are visibly highlighted without disrupting link handling.

Written by the indexing model from the issue text.