Make bibref query case-insensitive

See commit messages for more details.

This addresses tobie/specref#22
> FWIW, http://www.w3.org/TR/html/ and http://www.w3.org/TR/html5/
> point to the same resource. :)

Yeah, but my point is that ref "HTML" points (and has always pointed) to http://www.whatwg.org/specs/web-apps/current-work/ There are no time-stamped versions there.

> But that's not what this is about. Consider those references as opaque
> strings kept for legacy purposes only.

AFAICT ref-list.json has been created automatically from inconsistent data, so that's a very weak argument. I don't want to spend more time discussing this. Just tell me whether it's still a blocker for you and I'll fix those few cases manually even though I'm still convinced that it is a completely senseless exercise.


> Also note that given how Respec works, spec's URL are defined on the 
> client-side for drafts, and it's unclear to me whether or not google would
> catch those atm.

Sure, they would be in the text as well. Try, e.g., RFC6570 site:hydra-cg.com (there are no static specs there yet, all are ReSpec generated).