Hello cargo

Built on top of https://github.com/rust-lang/rust/pull/15181. https://github.com/steveklabnik/rust/commit/e52719291183d7b4f691a1997c69fd75b8101b07 is the only new commit, you may want to review that separately.

I'm not sure if the car analogy is too glib.
As I mentioned previously, no, it is not. However, setup is _complex_ and text is _hard_. My hundreds of hours teaching has shown a little bit more depth during setup goes a very long way.

This will move faster, now that the next section is actually getting into the language itself.