Add macro proto_library that calls protoc to generate code for grpc.
Add macro proto_library that calls protoc to generate code for grpc.

bazelment/trunk,duanguoxue/trunk,mzhaom/trunk,duanguoxue/trunk,mzhaom/trunk,bazelment/trunk,mzhaom/trunk,bazelment/trunk,bazelment/trunk,duanguoxue/trunk