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
Why is the vector (heap) allocation only a few bytes before the vector value itself (which is on the stack)?

It might be clearer to have these addresses be simpler and more easily distinguishable, e.g. `0x100` and `0x200` etc. so that people aren't having to spend (as many) cycles matching the addresses.

Also, having a clear distinction between the vector heap memory and the general other variables might be nice, since we're really focusing on what happens on the heap.