Intro redux

Because my '30 minute intro' was originally a blog post, the tone was a bit too light. It also was written a long time ago, and deserves a bit of a refresher for modern Rust. now that my work on the Guide is wrapping up, I want to give it a quick re-write as well.

This is not yet done, but I'm submitting it for feedback so far. I'd really like some comments on the ownership part in particular, which gets lower level than before, but is not strictly 100% accurate. Trying to strike a balance.

In general, I'm not sure I go into enough detail for those without systems experience, but am afraid of too much detail for those that do.

Rendered view: https://github.com/steveklabnik/rust/blob/intro_redux/src/doc/intro.md

/cc @wycats @nikomatsakis @brson etc
I agree with @huonw that this should probably be mentioned at least in passing. The only mention of "data race" is this sentence here and the conclusion at the end doesn't explain that rust has *zero* data races. I think it's ok to say it's a bit more of an advanced topic and can be explained later (insert guide here), but it should probably be mentioned as it's one of our biggest selling points.