[willing to PR] Use it to generate/deserialize `protobuf` (which is frequently used in place of json)?

[fzyzcjy]

Hi thanks for the lib! I am using protobuf extensively to replace JSON. For example, instead of returning a json from server, a protobuf is returned. Thus, it is very much needed to serialize/deserialize protobuf into custom data structures, like what json_serializable do for JSON. I am willing to make a PR, so could you please give some hints about where to modify the code?