Added
- Added `pyproject.toml`. [8](https://github.com/feos-org/feos/pull/8)
- Fixed modules of `SI` classes to make them pickleable. [8](https://github.com/feos-org/feos/pull/8)
Packaging
- Updated [`feos-core`](https://github.com/feos-org/feos-core/blob/main/CHANGELOG.md) to 0.1.5.
- Updated [`feos-dft`](https://github.com/feos-org/feos-dft/blob/main/CHANGELOG.md) to 0.1.3.