Optimize performance and SEO

[3top1a]

This PR is a bit larger but I tried to split it into multiple simpler commits.

Old lighthouse score: New score:

The old site transferred 908kB on load, the new one just 259kB.

Quick rundown of the changes:

• Added a simple description for search engines
• Marked links as User Generated Content (this site's reputation will not be influenced by the reputation of linked sites)
• Added robots.txt
• Changed the names from h3 to h2
• Added aria labels for accessibility
• Made images lazy load (only loads when the user scrolls near them)
• Made the browser preconnect to save time
• Added compression middleware

The only change needed to reach 100% on performance is to use webp instead of png/gif. Don't forget to add your site in Google's Search Console so it's visible.