Review W3C drafts/notes re: Accessibility API mapping and implement changes accordingly

[luketw]

Sort of a note-to-self so I don't lose the relevant documentation for these, especially when some of them are relatively new or recently updated - these ones in particular:

• WAI-ARIA 1.0 User Agent Implementation Guide (REC 2014-03-20) - (https://www.w3.org/TR/2014/REC-wai-aria-implementation-20140320/)
• HTML to Platform Accessibility APIs Implementation Guide (WG Note 2015-09-29) - HTML-AAPI
• The following "Accessibility API Mappings" drafts being produced in line with W3C's "HTML 5.1":
  • Core Accessibility API Mappings 1.1 (WD) CORE-AAM-1.1,
  • Accessible Name and Description: Computation and API Mappings 1.1 (WD) - ACCNAME-AAM-1.1
  • HTML Accessibility API Mappings 1.0 (WD) - HTML-AAM-1.0

Primarily for the priority of "aria-*" items in producing a accessibility API names and attributes, but also to be more fully up-to-date with ARIA things in general.