clientcompat tests for Twirp RPC

The executable here, jscompat-node.js reacts to the environment variable: USE_JSON. If this is set to 1 then the client will communicate with the TwirpRPC with JSON instead of protobuf. The input/output handling is identical in either case.

The generated files where generated from the .proto here, which is from: https://github.com/twitchtv/twirp/blob/e2117e5759cedf4aaaf7dfa919d6f162fc9726c8/clientcompat/clientcompat.proto