Excelrd

- Modify to use `pypa/build` for package build
- Add support for Python 3.9/3.10/3.11
- Drop support for Python 3.5/3.6
- Fix `MANIFEST.in`
- Add metadata to the package
- Remove `BYTES_IO` and `UNICODE_LITERAL` from `timemachine.py`
- Remove `setup.cfg` file
- Add `docs` extras

**Full Changelog**: https://github.com/thombashi/excelrd/compare/v2.0.3...v3.0.0

- Add support for PyPy

- Modify packaging
- Add `dev` extras

- Fix a `DeprecationWarning` about `getiterator`
- Add `.asc` files of packages to PyPI
- Drop Python 2 support
- Add Python 3.8 support