Add PyPI metadata, badges, and install instructions

Add readme, authors, classifiers, and project URLs to pyproject.toml.
Add PyPI version, Python versions, and license badges to README.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Fix license field for older setuptools compatibility

Use table form for project.license to work with the setuptools version
available on Python 3.8.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Merge pull request #26 from andravin/fix-25-sympy-support

Fixed #25 for Sympy 1.6.2