Fill in various "?" cells from the element and attribute tables (#245)

* add AXAPI mapping for pattern attribute

* add not mapped ping attribute

* update reversed

* update rows attr

* u element not mapped in AXAPI

* maxlength attribute not mapped in ARIA

* mappings for minlength attribute

* start attribute axapi

* playsinline attribute not mapped

* add not mapped referrerpolicy attribute

* add comment to required attribute

* axapi step attr not mapped

* update axapi for src attribute

* update link for style and link[title] attributes

* update scope attr

* srcset not mapped

source is not mapped
srcset on img elements is not mapped, only the baseline src is exposed.

* update type attr on button elements

* add data[value] not mapped

* label attr aria mapping

no direct mapping

* update content introducting attribute table

add note about “not mapped”

* size and sizes attribute mappings

* no mappings for sizes on img and source
* no mapping for size attribute on input
* refer to listbox if size > 1 on select element

* update input type mappings

* fix typo

* input[value] not mapped to ARIA

potential for this to change in the future per ARIA issue added as inline comment.

* update mapping table for disabled attr

should state to use WAI-ARIA mappings

* update spellcheck

update to use WAI-ARIA mappings

* update AX usemap

* cleanup title and add comments for future issues

* Add AX for span attr

add inline comment to update ARIA mapping ? for future issue.

* update tabindex to point to core aam

* corrects src UIA mapping

this was incorrectly listed as UIA does not map `src`.
closes #266

* adds changelog entry for this PR

Author: scottaohara