Version 3

[utrack]

With the protoc-gen-go v1.20.0+ and new gRPC generator breaking compatibility (see grpc/grpc-go#3828), it seems that a big refactoring process will be needed (and frankly, current code calls for it).

This is a good chance to implement some things in a better way and throw away some others: for example, tricky output rules pre---module flag.

This is an umbrella issue that will collect everything that will go to v3.0.0.

[bullgare]

If you need any help with that (like writing tests or code review) - feel free to ask.
Hope I will have time at nights :)

[wish-master]

+1 to @bullgare, @utrack I'm in

[utrack]

Thank you, guys!