Summary
- Added STIX v1.2 XML Schema and [Best Practice](http://stixproject.github.io/documentation/suggested-practices/) validation.
Updates
- Added STIX v1.2 schema
- Added best practice validation check for STIX v1.2 deprecations.
- Added best practice validation check for duplicate `id`, `timestamp` pairs
- Improved performance of best practice validation checks.
Links
- Download: https://pypi.python.org/pypi/stix-validator/2.2.0
- Documentation: http://stix-validator.readthedocs.org/en/stable/