Add support for cross_ref in property for exception
Fixup more tests
Fix doc string
Change keys into a quasi-compartment

- Due to how keys worked we'd have to spread the _parent_model variable
so I turned keys into a quasi compartment.
fixup buff tests
Extract method into model method
Add into_type for Ref enumeration
Add element by cross_ref to model

- You can search and verify element by crossref in model
Add cross_ref support for throws