BoxPart for Codio for installing Rust and Cargo by means of the rustup.sh script

Rust is such a new language with so many changes happening all the time that it is often useful to have the absolute latest bleeding edge version installed. Rust-lang.org provide a shell script that will do this, and this Box Part makes use of that shell script to install the absolute latest version. (As such, the version I've put in is just "latest" and there's no SHA1 because this will possibly change very regularly)