This either fixes or adds "FIXME" notes for any parts of the code that
corrode had trouble translating.
Namely there are a number of places members of the APDU struct(?) were
accessed which corrode failed to translate.
- Adds initial `Cargo.toml` (and `Cargo.lock` to `.gitignore`)
- Deletes `tool` (it seems hard to `corrode`)
- Moves `lib/tests` => `tests` (we should figure out how to translate them)
- Moves `lib` => `src` to match Rust conventions
- Renames `lib/ykpiv.rs` => `src/lib.rs` to match Rust conventions
- Adds copyright from `ykpiv.h` to the top of all `*.rs` files