the switch from package `hello` to `rust_pkg` is a little jarring; I'd use <var> but I don't see how. ALL_CAPS seems like a reasonable poor-man's <var>.
Three things in this commit:
1. Actually build the rustpkg tutorial. I didn't know I needed this when
I first wrote it.
2. Link to it rather than the manual from the
tutorial.
3. Update the headers: most of them were one level too deeply
nested.
