OBVIOUSLY DONT USE THIS AT THE MOMENT

These are rust bindings to the C reference implementations of the different keccak-based algorithms.

Currently the build script:

• clones the last version of the full XKCP library
• makes the static libkeccak.a library for generic64
• uses this as bindings

I'm not sure what the best way to offer support for different CPUs would be, perhaps manually through feature flags, or dynamically?