[racket-dev] tidy packages

This resumes the other thread started by John, and it is only meant as a 'this is good even if we can't define 'it'' message: 

As some of you know, we're trying to use Racket for a router. Until now I always wondered whether it would make any sense to have the clean separations into small, tidy or loosely coupled packages (for lack of a better word). This new project makes it abundantly clear why Eli is so right even if he has been so vague.