rust: add helper crate for generating raw bindings
This MR introduces the first bits of Rust to eventually support pure-Rust modules. :rust:
This MR mainly adds the helper crate that will be used to automatically generate the raw bindings.
It also adds the relevant files to the .gitignore and create the src/rust/
Cargo workspace.
One can see with this commit how the helper crate is going to be used.