Several suggestions

[newpavlov]

Currently I am playing with rust-crypto and one of things I am trying to do is to replace bundled simd.rs with this crate. Based on it I have several suggestions:

• Make struct fields (u32x4 and others) public. I don't see a reason why they should be private, while public fields make it noticeably easier to work with them.
• Make sixty_four structs public. It's imported into lib.rs but left private.
• Implement Shr and Shl (and probably other ops) traits for for u32x4 and other structs.
• If possible make crate use no_std. As far as I can see outside of examples only mem and ops used and none of vec, boxes or other std specific stuff.
• Implement or derive PartialEq and Eq for structs