[RFC] "http-types" breakage / additions / rework

My priorities are indeed correctness first, usability second, and performance third, but if I can improve performance, why not?

What I have right now is a ByteArray with a “case bitmap”, so that the ByteArray is always lowercase, and only when using HTTP/1 or pretty printing you would create a case sensitive result. But I do have one more idea which I want to check before committing to the current implementation.

The main point will be to not expose internals, so that when we find more performant ways to handle things, updating won’t break user-space.