Uses C for PAM authentication

[Timidger]

Currently, wc-lock uses C for PAM authentication because there is no good Rust crate for PAM. Even a lower level crate, such as pam-sys is poorly maintained because the API is added haphazardly, and without being generated at build time using e.g bindgen which would be preferable.

Since this is very security orientated, it would be nice to move this over to Rust since it's very, very possible my C code has bugs in it.