process: start publishing binary releases

[zombiezen]

(Opening this up as a backlog item, not saying we're going to get to this right now.)

This would improve the experience of first-time setup of protoc, since we can say just to download a few binaries. Not sure at what frequency these should be generated (maybe even every commit?).

[twoism]

Just tagging releases with the source code at the very least would be really helpful. gRPC does this https://github.com/grpc/grpc-go/releases and it makes dependency management much more reasonable. Especially when you have 10s of projects all with a random git SHA in their glide.yaml.

[dsnet]

We have begun tagging releases. I don't think it's necessary to keep an issue open regarding this.