Include djb's implementations in the benchmarks

[CodesInChaos]

It'd be nice if you included ref10 and amd64-64-24k in the benchmarks so it's easier to see if switching to your implementation is worth the effort.

Another interesting variant would be c code (without 128 bit ints) running as a 64 bit executable.

[floodyberry]

Included amd64-64-24k and amd64-51-32k, and benches on a Sandy Bridge CPU. Need to work on updating the SSE2 code now