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.
My recollection of the behaviour of `dir` is that it would take the `/w` switch to get it to print like that, the default arrangement is more similar to `ls -l`, plus an extra header.

Haven’t used `dir` for quite a long time…