Implement collapsable navigation menus like Wikipedia on moblie

The Python documentation table of contents is massive. It's unwieldy on a mobile device. A lot of that comes from itemising all the changelogs going back to 3.0 release. In and of itself, that's fine, but it takes a lot of scrolling to find anything. The indentation also isn't terribly clear to identify what is a subheading of what. Highly nested headings exacerbates this.

Collapsable TOC headings, used on sites like Wikipedia, would help tremendously with this. That way, mobile users could see a cleaner layout resembling the desktop TOC display, then be able to drill down into whatever topic they're looking for.

まず、テーマの目次のマークアップとモバイルナビゲーションのスタイルを調査し、現在の入れ子構造のレイアウトを Wikipedia の折りたたみ可能なナビゲーションと比較します。changelog のセクションを含め、モバイルで見出しをどのように展開・折りたたみするかを定義し、モバイルサイズのドキュメントビルドで結果を確認します。