Develop internal site diagnostics

[behoppe]

Issues
We have discussed several possible enhancements that probably involve some additional layer of process to evaluate site content:

• Integrate glossary entries and tags automatically Integrate glossary entries and tags automatically #103
• Checking for broken links (especially internally)
• Assessing glossary entries (esp how other articles use defn)
• Assessing tags (e.g. identifying clusters that we want to highlight)
• Cross-referencing articles that do not yet co-exist.
• Compiling bibliographic references

This issue is for developing an overall approach to enhancements like these. For example, do we write external programs? Or do we build "developer" functionality into the 11ty system? Or perhaps they are part of a headless CMS #100.

If we build developer functionality into the 11ty system, we might find these resources useful:

• https://jkc.codes/blog/creating-drafts-in-eleventy/ -- features ways to show drafts in developer mode
• https://pborenstein.com/posts/collections/ -- nice overview of managing collections (tags)

[behoppe]

Notable progress is incorporated into #164 which includes a defn-checker based on 11ty/eleventy#2565.

Need to double-check #169 and https://github.com/behoppe/www.opencilk.org/commits/behoppe-cilkplus-glossary to be sure that draft/dev-only articles are also here.