Add cargo-init, a cabal-like template generator

This independent module  initializes cargo repositories, much alike the functionality of "cabal init" for Haskell, or "dub init" for D. It allows the user to provide a name and license for their project, and have an instantly-buildable cargo package structure built for them.

cargo-init works both interactively and via command-line arguments.
(Answer: [yes](http://doc.rust-lang.org/master/std/io/fs/fn.mkdir.html).)

I think [`mkdir_recursive`](http://doc.rust-lang.org/master/std/io/fs/fn.mkdir_recursive.html) may be appropriate, but it's docs aren't so clear.