SipHash implementation for Rust

SipHash was recently removed from rust-core.

This crate brings SipHasher, SipHasher13 and SipHash24 back. It is based on the original implementation from rust-core and exposes the same API.

In addition, it can return 128-bit tags.

The sip module implements the standard 64-bit mode, whereas the sip128 module implements the experimental 128-bit mode.