Update setup.py version field to semantic versioning for PyPI compliance

[chigwell]

User Story
As a software developer maintaining Python packages,
I want to convert the version format in setup.py to semantic versioning
so that dependency management aligns with PyPI standards and community expectations.

Background
The current date-based version 2025.4.231259 in setup.py violates PyPI's semantic versioning norms, risking compatibility issues with dependency resolvers and confusing users. This format complicates version comparisons (e.g., pip install may misinterpret chronological ordering as API stability). The version field in setup.py is the primary artifact requiring modification. Risks include breaking existing CI/CD pipelines that parse the date format, necessitating clear release notes.

Acceptance Criteria

• Update version in setup.py to a semantic format (e.g., 0.1.0)
• Ensure PyPI badge URL in README.md reflects the new version format
• Add regex validation test in tests/test_mdextractor.py to enforce semver format (e.g., ^\d+\.\d+\.\d+$)
• Verify PyPI package upload succeeds using twine after version change
• Confirm version consistency between setup.py and PyPI metadata post-deployment