More useful index

[afred]

1. Decide which frontmatter to use:
   • Tags, a-z index terms, keywords, page title words?
2. Index should be a listing of whichever terms we're using from front matter, and under those, a sequential list of page titles.

Example:

1. Term 1
   • Page Title 1
   • Page Title 2
2. Term 2
   • Page Title 2

[laritakr]

@afred new browse page returns 404 error. Issue needs to stay open until fixed.