2. Improved robustness of StructureMatcher using linear assignment.
3. Improved primitive cell search (faster and more robust).
4. Cleanup of deprecated methods, including
   pymatgen.alchemy.materials.TransformedMaterial.undo/redo_last_transformation,
   pymatgen.core.site.Site.distance_and_image_old, Poscar.struct,
   StructureFitter and tests.
5. Miscellaneous bug fixes and speedups.