Improve reading experience: use remark plugins for markdown

[siman]

Interesting remark plugins for markdown

https://github.com/remarkjs/remark-normalize-headings https://github.com/mrzmmr/remark-behead https://github.com/remarkjs/remark-autolink-headings https://github.com/remarkjs/remark-toc https://github.com/remarkjs/remark-squeeze-paragraphs https://github.com/remarkjs/remark-slug https://github.com/remarkjs/remark-highlight.js

https://github.com/remarkjs/remark-unlink