Support Cloudflare-style resolution

https://developers.cloudflare.com/pages/configuration/serving-pages/#route-matching

> If an HTML file is found with a matching path to the current route requested, Pages will serve it. Pages will also redirect HTML pages to their extension-less counterparts: for instance, `/contact.html` will be redirected to `/contact`, and `/about/index.html` will be redirected to `/about/`.