* Prep for v4.3.0

* More updates for v4.3.0.

* rerun to build docs source map

- Move 4.1 docs to 4.2
- Update versions everywhere to 4.1.3 with release script
- Manually bump the shorthand version in package.json
- Add 4.2 to the versions docs page
- Update some redirects
- Fix tests asset URLs
- Bump Nuget and more

Running `./build/change-version.js v4.0.0-alpha.6 v4.0.0` fixed this,
so the version change script works fine. I'm presuming instead this
change was just omitted from 35f80bb1, and then wouldn't have
been caught by subsequent runs of `change-version`, since it only
ever replaces the exact old version string specified.