Appconfigpy

- Add `zip_safe=False`
- Update `[build-system]`
- Modify to use `pypa/build` for package build

**Full Changelog**: https://github.com/thombashi/appconfigpy/compare/v2.0.0...v2.0.1

- Make `ConfigItem` class to an immutable class
- Make `DefaultDisplayStyle` class an Enum
- Improve type annotations
- Drop support for Python 3.5/3.6
- Add support for Python 3.10/3.11

**Full Changelog**: https://github.com/thombashi/appconfigpy/compare/v1.0.2...v2.0.0

- Drop Python 2 support
- Add type annotations and `py.typed` to the package
- Add support for Python 3.9
- Add support for PyPy
- Add `.asc` files to the PyPI package
- Replace the logging library