This PR updates protobuf to 3.x.
To do that, it also replaces protobuf-codegen-pure 2.x with protobuf-codegen 3.x, which has the same capabilities. This version of the generated protocol API has a slightly different API, so the PR looks larger than it actually is.
This PR updates protobuf to 3.x. To do that, it also replaces protobuf-codegen-pure 2.x with protobuf-codegen 3.x, which has the same capabilities. This version of the generated protocol API has a slightly different API, so the PR looks larger than it actually is.