Make XSD validation namespace-aware and enforce the form defaults and
xs:all structural constraints that were previously ignored:
- targetNamespace is tracked: a schema's global elements are in its
target namespace, and an instance's root element must be in it.
- elementFormDefault / attributeFormDefault (and per-declaration form)
qualify local element and attribute declarations. The content-model
matcher already compares namespace URIs, so qualified declarations
now match only same-namespace instance nodes; attribute matching
became namespace-aware too.
- xs:all groups are checked at compile time: every member must be an
element occurring at most once, the group may occur at most once, and
nested model groups inside an all are rejected (a SchemaError).
When a schema has no target namespace the stamping is a no-op, so
unqualified schemas validate exactly as before.
Cross-namespace type references through xs:import resolve by local name
only; full multi-namespace type tables are not modeled.
Closes#78
