style: apply markdown formatting

[bo5o]

• add mdformat and markdownlint to pre-commit hooks
• configure mdformat and markdownlint for github flavored markdown
• auto-generate table of contents with proper document links/anchors
• wrap long lines
• avoid inline html where it is not necessary (e.g. ___ instead of <hr>)
• use special highlighting directives for Note blocks

[CKolkey]

Ooooo fancy. I dig it, might have to steal some of this for neogit haha