Show full program in tutorial with highlighted lines

[shaedrich]

As suggested in https://github.com/ponylang/pony-tutorial/issues/340#issuecomment-2128485356

Example: https://deploy-preview-552--pony-tutorial.netlify.app/types/classes

[netlify[bot]]

✅ Deploy Preview for pony-tutorial ready!

Name	Link
🔨 Latest commit	83938247117266c7db99bf06250277c041528b51
🔍 Latest deploy log	https://app.netlify.com/sites/pony-tutorial/deploys/66606ca2f92058000818fabe
😎 Deploy Preview	https://deploy-preview-552--pony-tutorial.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.