網頁動態目錄(dynamic TOC webpage)

希望在網頁中使用動態目錄的效果，方便讀者快速理解全文內容

Inspired by: https://www.bittbox.com/general-web-design/toc-website-trends

Here are some good examples:

1. https://tscanlin.github.io/tocbot/#contributing
2. http://gregfranko.com/jquery.tocify.js/
3. https://developers.optimizely.com/x/solutions/javascript/reference/index.html
4. https://pokeapi.co/docsv2/