A small, self-contained SHA512 and HMAC-SHA512 implementation in Rust.

Also includes SHA384 and HMAC-SHA384, that are just truncated versions of SHA512 with a different IV.

Optional features:

• traits: enable support for the Digest trait from the digest crate.
• sha384: includes support for SHA384 and HMAC-SHA384.
• opt_size: enable size optimizations. Based on benchmarks, the .text section size is reduced by 75%, at the cost of approximately 16% performance.