tech debt listing

[RobinQu]

This is a long running issue that tracks technical debts found in existing code base.

• transaction management in instinct-assistant services.
• ProtobufUtils refactoring Refactor protobuf with other header-only serialization library like flatbuffers #29
• RE2, ICU, or both?
• protobuf genearted classes are not header-only Refactor protobuf with other header-only serialization library like flatbuffers #29
• improving json context access Refactor protobuf with other header-only serialization library like flatbuffers #29
• stream api support stream interface implmentation #28