Ownership guide

This is a work in progress, but this should get *extensive* review, so I'm putting it up early and often.

This is the start of a draft of the new 'ownership guide,' which explains ownership, borrowing, etc. I'm feeling better about this framing than last time's, but we'll see.
I think this might be better as:

```rust
static FOO: int = 5i;
let x: &'static int = &FOO;
```

i.e. the static data actually lives forever. It's not inconceivable that `let x: &'static int = &5i;` could work, i.e the compiler detects that `5i` is a compile time constant and implicitly promotes it to static data, hence, for the example currently written, the `static FOO` isn't necessarily required.