WIP: Fix subdivide functions

[haesleinhuepf]

Fixing the tests in this branch closes #57 . Before merging, remove the _ at the beginning of the three _subdivide functions.

Just run

pytest

Output (excerpt):

=============================================== short test summary info ===============================================
FAILED napari_process_points_and_surfaces/_tests/test_vedo_functions.py::test_subdivide_loop_vedo - assert 3324 < 0
FAILED napari_process_points_and_surfaces/_tests/test_vedo_functions.py::test_subdivide_butterfly - assert 3324 < 0
FAILED napari_process_points_and_surfaces/_tests/test_vedo_functions.py::test_subdivide_linear - assert 3324 < 0
===================================== 3 failed, 16 passed, 216 warnings in 20.56s =====================================