Add REDB

[phikal]

And as a parallel suggestion to #41, I also made this site, http://redb.org.uk/ or https://github.com/phikal/REDB, which is supposed to be like a collection of regular expression tasks, with solutions. Sadly I haven't gotten around to fill it up with actual tasks, so it's a bit meager as of now, so I don't expect it to be added to the list at once.