[TRACKING] Tracking Issue for RFC 0005

[andrewherren]

Implementation / rollout tracker for work items in RFC 0005 which standardizes serialization logic and adds structure to support version updates. Specifically, this RFC:

1. Standardizes JSON format for BART and BCF and in R and Python
2. Implements a "schema versioning" system to better track / manage future changes to the serialization format
3. Makes clear when cross-platform deserialization works and explicitly rejects all other cases
4. Allows for continued sampling without a JSON roundtrip