Initial draft of automatic docs

[joshuatorrance]

This PR contains some simple scripts to grab schema from the schema repo and build some docs from them.

The script will be set up to run when there's a commit to this repo (i.e. doc templates or scripts have changed) and probably when some still-to-be-determined activity occurs in the schema repo (although a manual run of the script could work too).

Still to do:

• Update schema URL to the main repo (once new schema PR is merged)
  • Is there a smart way to point to the most recent version of the schema? Github releases maybe?
• Take a look at the ordering of the rows in the table, doesn't look right at the moment
  • Hard code order? Alphabetical?
• Remove "comments" from global table? Would look better on my monitors and info could be in description.
• Add required as a column
• Lists with one element should not be dot points
• Figure out what (if any) activity in the schema repo should trigger a rebuild
• Flesh out the doc more fully. More descriptions, explanations etc.
• Consider moving some of these points to new PRs/issues
• Check directory and file paths are correct
• Create artifacts on release?
  • pdf - should be created by readthedocs, how to get as release artefact?
• Zenodo integration on release (needs a release to trigger)
• readthedocs
• rename repo?