Add binary encoding/decoding to backup

Add a binary encoder/decoder like https://github.com/hashicorp/go-msgpack. We need something that is binary encoded and a bit denser than JSON. The reason for this exercise is more to get the Encoder/Decoder interface fleshed out with reference uses. Having a binary format should result in much smaller backup files.

Start by locating the backup handling and any Encoder/Decoder interface references in the repository, then compare the intended behavior with hashicorp/go-msgpack. Done means backup data can be encoded and decoded in a binary format, with smaller files than JSON and reference uses for the interfaces.

Written by the indexing model from the issue text.