More WIP: Aiming for simply getting something to test with

Current estimate at rather ideal case speedup: 14% (see silly loop in
test file). That is after subtracting a socket startup time and if
loading the optimizer module also in the base variant (without actually
optimizing). So really, this is probably the very best case.

Commonly, the speedup will be much less since not only constant-key hash
accesses will be going on. Maybe unrolling some of hv_common_key_len
could help, but, well, maybe better not to go there.