Fix module file, remove extra README.md and fix some docs

The module file had the wrong revision in it for starters. And there was some
missing items from the .gitignore.

The extra README.md in spec/system was getting extracted as the main README
on the forge so I remove it, moving the content that was not duplicated
already into README.md.

I took the opportunity also to finish the documentation in the Reference
section of the README to make sure all classes and defined resources are
documented.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge branch 'maint/changes_before_210_release'

* maint/changes_before_210_release:
  Fix module file, remove extra README.md and fix some docs