Port changelogs

[LWinterberg]

https://wiki.audacityteam.org/wiki/Audacity_Versions has changelogs for (almost) all past versions, and it's one of the last still-useful non-outdated resources that haven't been ported over yet. As it turns out, it's reasonably painless to do using Gitbook's "import" function from the right-hand sidebar (or 3-dot menu on smaller screens):

I started a branch here which you can contribute to: https://app.gitbook.com/o/-MhmG2mhIIHTtQPuHV_k/s/-MhmBVzGzh8SctWQ6jPR/~/changes/ajm1Za9MrwdVvU8EM1ZM/changelog

NB:

• The importer sometimes imports the table of contents. Gitbook already generates one, so that can be deleted.
• For releases between 2.1.3 and 3.0.4, the actual changelog is in the new features archive, rather than the release notes - the idea back then was that the release notes would be updated after the release with known bugs and workarounds and such. If you want to, you can import the release notes for those versions as a subpage to the changelog, but I don't see nearly as much value for that