RpcExplorer: Interactively build RPC requests

RpcExplorer is a curses tool that allows the user to search for service methods defined in protobuf and interactively build and issue requests.

I built it a few months ago, and my team at Square has been using it to save time during both development and debugging when interacting with gRPC and proto-over-http servicse defined in protobuf.

If you use protobuf-based services, please feel free to play with it and let me know what you think!