text: Title: Generate lists of pages based on tag metadata
  Body: It would be useful if users could attach **tags** to certain pages, and then use these tags to generate lists of pages that fall under that tag. This is a common thing to do in blogging platforms, and may be useful here as well.
  
  [ABlog kind-of supports this](https://ablog.readthedocs.io/en/latest/), but it uses a directive rather than page-level metadata.
  
  Ideally, people would be able to include metadata at the top of their pages like:
  
  ```
  tags: tag1, tag2
  ```
  
  and then include a list of pages with those tags via something like:
  
  ````
  # To generate a list of pages that have `tag1` in their metadata
  ```{tag-list} tag1
  ```
  ````
  
  