This release includes the following changes:
- #258 Ignores empty values for optional fields (@khdesai)
- #259 Adds support for lang granular markings (@emmanvg)
- #261 Prevents instantiation or serialization of TLP marking-definitions that don't follow the spec (@emmanvg)
- #262 Supports actual objects in _valid_refs instead of just strings (@khdesai)
- #264 Supports accessing objects in bundles via STIX Object IDs (@khdesai)
- #274 Fixes bug parsing bundle containing custom objects (@chrisr3d)