This improves the algorithm for searching for pages. It now works like:
1. If pathname ends with /
1. Look for PATHNAME/index.astro
1. Look for PATHNAME/index.md
1. else
1. Look for PATHNAME.astro
1. Look for PATHNAME.md
1. Look for PATHNAME/index.astro
1. 301
1. Look for PATHNAME/index.md
1. 301
1. 404
