- Add pickle support to PsType
 - Add `__canonical_args__` protocol for more efficient uniquing
 - Write extensive documentation around PsTypeMeta
 - Refactor data types section in docs

 - Introduce metaclass PsTypeMeta
 - Refactor __args__ protocol to exclude const
 - Move PsType and PsTypeMeta to types/meta.py
 - Rename basic_types.py to types.py
 - Adapt test cases to check for identity