Feature Request: Profiles specified via protobuf

Currently, it's a little tricky to figure out how to write an extension and/or profile. Assuming the users of this library are already familiar with protobufs, I'd say it'd be simpler if an extension could be generated from a protobuf file (i.e. if `generate_protos_from_config.sh` accepted a `.proto`).

That said, I am not sure about whether in general a `.proto` has "too much" or "not enough" information to generate an extension (as I still figure out how to write an extension and profile).