Add tooltips for code comprehensibility

[cyrusae]

• [x] Add the CSS into the master sheet
• [x] Add to the generated HTML
• [x] Slightly harder: Use the full name instead of the shortcode?

[cyrusae]

Someday goal: figure out if I could determine tooltips dynamically instead of hardcoding them in. useEffect on marks maybe?

I would try that tonight but I am worried about interference with the fact that I'm using innerHTML direct. Hardcode tooltips are present, anyway.