Release v0.15.0

What's Changed

• Fix .readthedocs.yaml by @phackstock in #303
• Fix pydantic warnings by @phackstock in #308
• Add link to ISO homepage by @phackstock in #306
• Improve test coverage by @phackstock in #310
• Use multiple external repos for definitions and mappings by @phackstock in #311
• Collect duplicate code errors by @phackstock in #314
• Apply black 24.1.1 by @phackstock in #318

Full Changelog: v0.14.0...v0.15.0