v0.1.4 - First public release

First public atomref release: a lightweight, pure-Python package for curated, provenance-aware atomic reference data.

• Includes element metadata and named datasets for covalent, van der Waals, and atomic-radius values.
• Provides typed policies with overrides, fallbacks, custom sets, and transfer-based completion.
• Added provisional X–H bond-length support via xh_bond_length, csd_legacy_xh_cno, and XHPolicy.
• Transfer models now support datasets, custom sets, and policies as sources.
• Added safeguards for nested correlations, transfer-depth tracking, and robust cycle detection.
• Documentation, changelog, and roadmap were cleaned up and synchronized across the repo.