Initial commit of ioreg! syntax extension
ioreg: Mark accessors with allow(missing_doc)
ioreg::setter: Fix clear flag docstring
ioreg::accessors: Add docstring to `get()`
ioreg: Allow enums to lack documentation
ioreg: Allow register unions to lack documentation
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
Merge pull request #108 from bgamari/ioreg-rebased

Added new ioreg syntax extension