New f1600x4

[bwesterb]

Instead of using intrinsics and full unrolling, this uses a four-round unrolled version adapted from the one I wrote for Cloudflare's CIRCL library:

github.com/cloudflare/circl/simd/keccakf1600

This is about 10-20% faster on my notebook. We'd better check whether that's also true for other systems as well before merging.

[thomwiggers]

This also means it no longer works on Windows.

[bwesterb]

@thomwiggers Any suggestions how to advance this? (Given you are facing the same troubles with Kyber & Dilithium.)

[thomwiggers]

The Kyber/Dilithium AVX2 implementations are simply marked as not supported on Windows. It would still be a shame to drop Windows support from this otherwise mostly (bar VLAs) portable plain-C implementation.