v0.4.0

What's Changed

• Update ISO standard contributor table by @Max-Vermeir-ABBYY in #72
• improve virtual text schema, nesting, versioning & prerelease tooling by @vagenas in #73
• enhance support of captions, cross-references, and hyperlinks by @vagenas in #74
• align validator with spec; defer planned features to Appendix B by @vagenas in #75
• refine repo layout by @vagenas in #76
• add <label> and <index>, specialize <picture>, static PyPI versioning, and spec/schema cleanup by @vagenas in #77
• Update spec.md by @PeterStaar-IBM in #78
• add CI, enhance dev env and validation tools by @vagenas in #79
• refine <picture> subclassing, update examples by @vagenas in #80
• add version to spec, rescope example showing planned feature by @vagenas in #81
• improve <location> handling, various spec refinements by @vagenas in #82
• enforce field scope rules, expand recommendation guidance by @vagenas in #83
• update spec example picture, add fixture by @vagenas in #84
• refine public API and reorganize validator docs by @vagenas in #85
• prepare release v0.4.0 by @vagenas in #86

Full Changelog: v0.3.0...v0.4.0