Add a changelog for tracking specification changes across versions

[kgryte]

This PR

• adds a changelog for tracking specification changes across versions. As the v2022.12 revision is the second edition of the array API standard, the changelog only includes changes since the initial specification release.
• distinguishes between "updates", "additions", and "errata". For the most part, errata are either typo fixes or areas of underspecification/need for clarification.
• addresses part of Add a changelog #507

[rgommers]

Thanks @kgryte. This will be quite useful for implementers. A few comments here and inline, with as common theme aiming to be more explicit and easier on the reader. It's a little bit terse and not as easy to navigate as it could be.

It would be useful to add a short description at the top. Something like "This changelog is organized by specification version, noting all changes with respect to the previous version. Within the section for a specific version (e.g., v2022.12), separate sections are used for (a) changes to existing APIs and requirements, (b) new APIs and new requirements, and (c) errata".

I didn't review for completeness yet.

[rgommers]

We had a look at this with a few folks during a call today - all looked clear and complete. So in it goes

[asmeurer]

Is #497 mentioned here? I don't see it.

[asmeurer]

I would suggest adding this to the site itself somewhere.

[kgryte]

@asmeurer #497 is mentioned in multiple locations: https://github.com/data-apis/array-api/pull/574/files#diff-06572a96a58dc510037d5efa622f9bec8519bc1beab13c9f251e97e657a9d4edR15-R18.

[rgommers]

I would suggest adding this to the site itself somewhere.

Good suggestion @asmeurer, I've opened gh-577 for this.