Merge branch 'jakecobb-python-container-memory'

* jakecobb-python-container-memory:
  Better name for container back-reference attribute
  Python - Struct spec. for container owner
  Python: Avoid container owner check for value types
  Python: Init container owner attribute in thread-safe way
  Python: Use PyObject_SetAttr instead of PyObject_GenericSetAttr for back-ref
  Python: Cleanup container back ref
  Python: Keep reference to owning container during element access