Support RustCrypto KEM and Signature traits

[thomwiggers]

RustCrypto has finally decided what traits they want to have for KEMs and Signature schemes. We should probably make sure our types implement those traits as well.

See also rustpq/pqcrypto#40

[SebastianFaller]

Hi Thom, is this still relevant? I could give it a shot.

[dstebila]

Hi Sebastian! Thom is working on other projects now, so I'm not sure he'll be able to respond. I don't have much Rust expertise, but I would say that if you have Rust expertise and see a need for it, then go ahead!