Add/update implicit ARIA roles and allowed ARIA

[Malvoz]

Close #149.

Adds/updates implicit ARIA roles and allowed ARIA.

Notably:

• The map element is now implicitly role="map";
• The feature element is now implicitly role="feature"

The ARIA of each element is subject to change of course, I suggest opening new issues to discuss the accessibility considerations of each element when/if needed.

Preview (in comparison to WHATWG HTML's accessibility considerations)

HTML spec:

MapML spec:

For authors

The HTML spec links For authors (for the html element in this case) to https://w3c.github.io/html-aria/#el-html:

The MapML spec can't (at least not consistently) link to ARIA in HTML because it defines new elements (e.g. the mapml element), we can include the ARIA in a details element instead:

For implementers

The HTML spec links For implementers (for the html element in this case) to the html element in the HTML Accessibility API Mappings: https://w3c.github.io/html-aam/#el-html (the site's CSS is currently broken so you'll have to collapse the sidebar to view the entire table).

The MapML spec doesn't yet have any Accessibility API Mappings, perhaps the most appropriate thing to do is link to the GH issue:

[prushforth]

Looks good, lots to discuss. Sorry I overlooked this until now.