Add most AVX2 intrinsics.
Add most AVX2 intrinsics.

graydon/rust,GBGamer/rust,aidancully/rust,dwillmer/rust,dwillmer/rust,graydon/rust,GBGamer/rust,dwillmer/rust,aidancully/rust,dwillmer/rust,graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,dwillmer/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,dwillmer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,dwillmer/rust,dwillmer/rust,aidancully/rust