Versioning in the spec URLs

[asmeurer]

#394 gives a way we can add a version menu to select different versions of the spec once we release things.

We should decide how we are going to name the versions in the URLs, so that we don't end up changing things and breaking the URLs. For example https://data-apis.org/array-api/latest/index.html

My suggestions:

• Right now where the URLs say latest we should write the full version number (e.g., https://data-apis.org/array-api/2022.02/index.html)
• We should continue to have latest, which always redirects to the latest version of the spec. I'm not sure if it should be a literal redirect or just a copy. If we did a redirect, any URL would always redirect to something that will be stable and always point to that exact version. With no redirect, a "latest" page will give a URL that will change whenever we do a release. The effective difference is the behavior when someone copies the URL from their browser.
• We need something that can point to the development version of the spec. I would suggest using something like draft or development.

The main index page should always point to latest. We might also consider adding headers to the development version that warn people that it isn't a released version.

[kgryte]

This should now be addressed. Namely,

• latest redirects to the latest specification revision.
• draft serves as the development version.
• the main index.html page redirects, similar to latest, to the latest specification revision.