Consider deprecating old Leaflet versions docs, and automate publishing

Currently dealing with Leaflet docs causes quite a bit of confusion:

• Since reference.html is built locally and committed to the repo, we often get PRs on the generated files rather than sources for docs fixes.
• Updating docs for a release is a quite involved manual process — ideally this would be completely automated.
• Old version docs might show up in Google search results instead of latest docs.
• Keeping generated files in the repo (and we have quite a few, including old versions) is a bad practice.

We introduced links to old Leaflet docs back in 2012, when Leaflet was v0.3. Now that it’s way more stable and mature and breaking changes are extremely rare, I think we can drop the old versions and only have one reference docs reflecting the latest version.

Also, now that we’re using GitHub Actions, automating the docs publishing when tagging a release seems quite doable. cc @jonkoops @IvanSanchez

[Malvoz]

There are snapshots of all the reference versions in the Internet Archive’s Wayback Machine:

• 0.7.x
• 1.0.3
• 1.1.0
• 1.2.0
• 1.3.4
• 1.4.0
• 1.5.x
• 1.6.0
• 1.7.1
• 1.8.0

+1 for deprecating old versions docs.

[Falke-Design]

I think we should replace it web archiv links or at least suggest that the versions can be found in the web archiv