- Only basis balls are exported, as they represent the resulting mesh.
As a result the mesh is written to Alembic using the name of the basis
ball.
- MetaBalls are converted to a mesh on every frame, then an
AbcMeshWriter is used to write that mesh to Alembic.
It's now less confusing (for example, using nr_of_samples directly,
instead of using 1 / 1 / nr_of_samples). Might also have fixed a bug.
Also added unittests.
Also replaced the bool param "to_yup" with "AbcAxisSwapMode mode", so that
it's more explicit that axes are swapped.
Also added unittests for create_swapped_rotation_matrix.