Release v0.21.0

[chrismaddalena]

Version updates for release.

[augmentcode]

🤖 Augment PR Summary

Summary: Prepares the repository for the v0.21.0 release by updating versioning and release notes.

Changes:

• Added a new CHANGELOG.md following a Keep a Changelog-style structure for the 0.21.0 release.
• Updated CHANGES.rst with detailed 0.21.0 release notes (performance improvements, InlineImage fixes, header/footer delimiter fixes, and test coverage additions).
• Bumped the runtime library version in docxtpl/__init__.py from 0.20.2 to 0.21.0.

Technical Notes: The project uses Poetry dynamic versioning, sourcing the package version from docxtpl/init.py.

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[augmentcode]

Review completed. 1 suggestion posted.

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[augmentcode]

CHANGELOG.md:8 — Keep a Changelog entries are typically formatted like ## [0.21.0] - 2026-06-15; using * 15 June 2026 may break tooling that parses changelog headings and it’s also inconsistent with CHANGES.rst’s ISO date format.

Severity: low

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