Clean up original GOD generated code

- improve use of flags by using generic functions to set/get,
  and compute offsets from values, instead of defining them
  coherently
- add [[nodiscard]] where appropriate
- avoid comparing SmartRef to 0
- have setters return reference to *this
- declare operator<< into the smallest possible scope so it does
  not pollute the global namespace -- and implement in in the .cpp
  file instead of in the header file. Also, prefer '\n' over std::endl
  to avoid flusing the stream midway