Rust-based USB U2F library

We've written our U2F library for Firefox in Rust, a safer systems-oriented
language. It's cross-platform, supporting Windows [1], Linux, and OSX.

https://github.com/jcjones/u2f-hid-rs

With a recent Rust compiler installed (call rustup update) you can try it
out with:

git clone https://github.com/jcjones/u2f-hid-rs.git
cd u2f-hid-rs
cargo build
cargo run --example main

It exposes a C API; we'll have instructions on how to link against it
somewhat soon, as we finish up that part.

[1] We actually just broke Windows, but we'll fix it really soon, I promise!

Issues / patches are certainly welcome.

Cheers,
J.C.