new lexer request: csv

I'd like to see the addition of a CSV lexer so I can highlight CSV data in blog posts, wiki articles, and documentation. It's basically about displaying delimiter characters, quoting characters, and the actual data differently to be easier to skim through.

This is likely to have the same problems that our sql lexer has -- namely that there are multiple, incompatible standards.

Maybe there should be a lexer for each dialect of CSV and SQL?