- Remove no longer needed `acme-challenge` file
- Set title, description, social image, logo, etc. for SEO
- Use extensionless permalinks (old links still work)
- Cleanup `_config.yml`
- Import latest `_layouts/base` from https://brew.sh
Bare URLs are auto-linked on GitHub but not on docs.brew.sh, so I added
angle brackets around them where appropriate. Also converted
Markdown-linked URLs for clarity.