Spinspg

- Drop support for Python 3.8
- Fix typo in scripts/generate_spin_point_group_table.py by janpriessnitz

- First release version

- Fix spin symmetry search and add table of nontrivial spin point-group types [[2]](https://github.com/spglib/spinspg/pull/2)
- Tabulate 598 spin point group types
- Fix eigenvectors for spin-only group search
- Fix to correctly search complement in nontrivial spin space group search
- Add note for spin point group and glossary

- Add functionality to find spin symmetry operations
- {func}`spinspg.get_spin_symmetry` returns spin symmetry operations from a given spin arrangement
- {class}`spinspg.spin.SpinOnlyGroup` represents a spin-only group.