Generator for steamlang and protobuf

We generate Go code from SteamKit protocol descriptors, namely steamlang files and protocol buffer files.

Dependencies

1. Get SteamKit submodule: git submodule update --init --recursive.
2. Install protoc, the protocol buffer compiler. At the moment, we use Protocol Buffers 3.15.8.
3. Install proco-gen-go: go get github.com/golang/protobuf/protoc-gen-go/. At the moment, we use 4c88cc3.
4. Install the .NET Core SDK (3.1 or later).

Execute generator

Execute go run generator.go clean proto steamlang to clean build files, then build protocol buffer files and then build steamlang files.