Issue #699 since fixed. Nearly a x3 perf improvement.
Using --release-fast.
Sha3_256 (before): 96 Mb/s
Sha3_256 (after): 267 Mb/s
Sha3_512 (before): 53 Mb/s
Sha3_512 (after): 142 Mb/s
No real gains from unrolling other initialization loops in crypto
functions so have been left as is.