New features
- Optional OBJ loading with `pip install lacecore[obj]`.
- Add transform methods.
- Add group selection.
- Add `apex()` method.
- Add `vertex_centroid` and `bounding_box` properties.
Bug fixes
- Pass through `face_groups` when returning a new mesh.
- Reject invalid `point` from selection methods.
- Avoid scrambling correspondence with inconsistent triangulation.