clarify 4.02.* releases

4.02.md: Set the title to 4.02 instead of 4.02.1 to indicate the page
regards all 4.02.* versions. Also add info about previous minor
release 4.02.0.

Add 4.02.0.html and 4.02.1.html as redirects to 4.02.html.
Merge branch 'master' of github.com:ocaml/ocaml.org