Fix typo.
Test get_enclosing_sphere() of Vector3Ds.
Check constructor failure cases.
Test get_transformation_aligning_pair() failure case.
Make a usage check.

The check should be fast, and is checking user input.
Test Connolly surface with colocated atoms.
Remove redundant code.
Test endian functions.
Correct description.
Add missing tests for namespace methods.
Add missing test for ReferenceFrame3D methods.
Add missing docstring.
Add basic tests for Reflection3D class.
Add tests for Rotation2D.
Test Segment3D.
Test SphereD<N> operations for unusual N.
get_bounding_box() doesn't currently work for SphereKD.