2.0 pre and post-release work

[klebba]

Tasks to complete pre-release

• Decide: remove support for ifDefined and repeat, or continue to support as deprecated features (and all related work, e.g. removing comments and other complexity)

Tasks to complete post-release — #215

• review docs; simplify, clarify
• review error messages; we have a list in Minor language tweaks to x-parser error language #248
• provide more pragmatic examples in /docs/EXAMPLES.md or similar
• think about the future of DocumentFragment support
• unleash Claude on the source
• review array and map validation (e.g., we could relax errors in some cases)