- Support AKN 3.0 namespaces
- Produce URIs with `akn` prefix by default (backwards compatibility
maintained)
- Support all Akoma Ntoso document types
- Start FRBR URI work component with `!` (eg. `!main`)
- FRBRcountry uses full country code from the FRBR URI
- FRBRnumber uses number portion from FRBR URI
- FRBRdate for FRBRWork contains the date portion of the FRBR URI
- Include AKN 3.0 schema and support for validating against the schema
- The elements returned by `components()` are now `attachment` or
`component` elements, not the inner `doc`