Protobuf message and service definitions.
Makefile generates golang message and service stub implementations into
//go/gen/proto/. The generated code is checked into the repository.
Dependencies are git submodules in //proto/third_party. You need to build
protoc in //proto/third_party/protobuf by running bazel build //:protoc from
that directory. Currently tested with bazel version 0.28.0.
You also need to run go build -o ._protoc-gen-go ./protoc-gen-go in
third_party/golang-protobuf.
Dependency tracking and hermeticity here poor.
$ make
or potentially
$ make clean all