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.
So, this is a good question. I've been using `**`s like index terms, which may not even be a great idea. I've always used it to highlight the word itself, and not the plural aspects.

This could be totally, 100% off base.