Update "Changes Since the Previous Draft"

[Malvoz]

• [x] Reorder some of the items (I had mistakenly added one or more entries to the top of the list at some point)
• [x] Reverse the visual order such that latest changes are on top and no need to scroll down to see the latest change
• [x] Add date for all changes (git blame history is fun) such that implementers can more easily track if they're up to date or not
• [x] Rename "Changes Since the Previous Draft" to "Changes" (aligning with others spec, also not sure if "Previous draft" implies version numbers)
• [x] Use <section> so that Changes is included in the TOC

[Malvoz]

The <summary> for the Changes section's details is now named Substantial changes to this specification with the intention that we only add entries if they're substantial and mostly important from an implementer's or reviewer's perspective. Thus I've removed the entries:

Add Google Translate widget

Add WICG link