Script to run validations from command line + docs

The script `validate.py` runs validations from the command line (no significant changes required for refactored code - hurrah). There are a couple of tweaks to reporting and intialization in `validator.py` so that it will work well with the command line script. These _should not_ affect the existing function of `validator.py`... Not sure these are quite ready to go in because we could perhaps do something tidier but that might mean larger changes or changes that would affect the current function, doing a pull request because that seems the easiest way to package for review.