Consider re-architecting packages a bit

[dslmeinte]

• Make separate package for low-level serialization chunk “stuff” – types and low-level functions.
• Simplify core package w.r.t. InstantationFacade (which is another term for “factory”) and ExtractionFacade.
  • Maybe move M3-specific “stuff” out to a separate package? (Named m3?)
  • We could even strictly separate M1-, M2-, and M3-“stuf” like we did for the C# version.