adding a zeroize trait for blockbuffers so that blake2 can have zeroize too (not zeroizeondrop- just zeroize)

[laudiacay]

No description provided.

[laudiacay]

oof. what should i do about this namespaced feature/nightly thing? @tarcieri

[laudiacay]

RustCrypto/hashes#87 (comment)

the blockbuffer doesn't expose the underlying genericarray, or even allow you to have a mutable slice to hook zeroize up to. there are some weird setter methods but i am concerned that might get optimized out by the compiler.

i could alternatively add a method to pull a mutable slice out of mutable blockbuffers, or expose a genericarray, let me know which one is preferable to this.

[tarcieri]

If you just remove the entire [features] section I'd think it would be fine.

Namespaced features aren't MSRV-compatible, as they require Rust 1.60. The MSRV being tested in CI is 1.56 (although it doesn't seem to be correct in the README.md)

[newpavlov]

Closing in favor of #963