Better hierarchy in S3 dist & patch buckets

Fixes #65.

We should be able to accomplish a smooth upgrade transition with this (though that probably doesn't even matter at this point). I think we can do that by first generating releases & patches for this new version using the old generator & builder, then rebuilding using the new `hkdist`, then pushing new code to the generator once those steps are done.

Might not be worth the trouble though since ~nobody should be using these binaries yet.