Merge pull request #125 from bgamari/master

platformtree: Track rustc changes

Reviewed-by: farcaller
Rakefile: Fix build_docs rule

Need to define library path; not sure how this worked before.
Rakefile: Add ioreg to build_docs
ioreg: Add documentation
Move the `ioreg!` macro to `ioreg_old!`

Indentation alignment isn't corrected, but the `_old` suffix is ugly
anyway.
Merge pull request #127 from bharrisau/ioreg_rename

Move the `ioreg!` macro to `ioreg_old!`
Merge pull request #108 from bgamari/ioreg-rebased

Added new ioreg syntax extension
ioreg: Add dump support
k20::{sim, pin}: Port to ioregs!
k20::uart: Port to ioregs!