Let's use a delegate object for constraints

I really need to get out of the habit of building things that aren't my
problem to solve. Next up, working on constraint rulesets. I'm not
really happy with how they work and the DSL (if I can go so far as to
even call it that) is super-clunky. I don't think I want the rules to
inherit at all, either, since the typical Record doesn't actually need
these at all -- only railsified RecordDelegates do at the moment.