Add initial Rust support

Downloads the latest Rust nightly and Cargo nightly, installs them and runst `cargo build` and `cargo test` by default.
I'm not sure if the split here is needed, since `cargo test` will also build the necessary things, but I suppose this divides the output a little bit.

Another option would be to add `cargo build` to the install method instead, since it will download any dependencis.