Implementation of protobuf-go-lite

[paralin]

This issue is intended to organize anyone who wants to contribute to this effort.

I have forked go-protobuf and dropped everything that is not referenced by protoc-gen-go.

protoc-gen-go has been renamed to protoc-gen-go-lite

Now the task is to adjust protoc-gen-go-lite to generate just the bare minimum structs without importing "reflect."

[paralin]

This is now complete! Also see the vtprotobuf-lite repo