Fresh proposal + sample markup for annotations via aria-detailstype

Please see the attached self-documenting HTML file. Each element with
aria-details has a matching aria-detailstype, and the aria-details points
to an element within the page. View source to see the markup.

I worked to keep this consistent with the annotations spec motivations
vocabulary and open for future expansion possibilities.

Would love to hear feedback.

Thanks!
- Aaron