Log Message:
py-cybox: updated to 2.1.0.21

Version 2.1.0.21
- New API Objects Support
- 8 New Objects API Classes
- 12 New Common API Classes
- Observable DefinedEffects
- More tests to cover new or existent objects
- Update documentation and coverage
- Rename module cybox/objects/{win_user_object.py → \ 
win_user_account_object.py} for consistency
- Some objects have been revised for TypedFields and/or new properties are now \ 
available

Version 2.1.0.20
- Fix parsing if algorithm, compression_mechanism, or encryption_mechanism are \ 
not present in Factories
- Factory classes now have a register_extension method decorator to extend API \ 
classes for the pack/unpack functionality
- The factory will fallback to the Base class when no mapping is found

Version 2.1.0.19
- Implement the Packaging attribute from Artifacts as a TypedField
- Fix a wrapping problem with one of the helper methods for ipv4 observables

Version 2.1.0.18
- Add missing methods to ListFieldMixin.
- Fix handling of empty Hash values.