cargo 3ds new and init commands

[ian-h-chamberlain]

Since cargo new is a convenient way to start a new project, I thought it might be useful to have a cargo 3ds new as well, to try and make it even easier to get started. This definitely isn't a necessary feature, but it might be nice to have to simplify the setup.

We could probably piggyback off plain cargo new --bin (forwarding arguments), then just modifying main.rs and Cargo.toml to add the dependencies on ctru and do some basic setup of Gfx and a Console to get a hello-world going.

Same all applies for cargo init, I think. Finding the directory would be slightly trickier but probably not too bad.

[AzureMarker]

Might also want to add a rust-toolchain/rust-toolchain.toml file so it uses nightly.