Auto merge of #5171 - flip1995:deploy, r=Manishearth

Improve deployment and documentation

**This should be merged shortly after** #5172

This extracts the python code that generated the `versions.json` file and now sorts the versions. in addition to that it improves the order on the website, respecting the new `rust-*` directories.

The new appearance of the documentation site can be previewed here: https://flip1995.github.io/rust-clippy/

changelog: Add documentation for Clippy stable releases at https://rust-lang.github.io/rust-clippy/