Build Equivalence Table Two Z Slices at a Time

[William Silversmith]

For very large volumes, it might be helpful to be able to provide a facility for processing Z slices in sequential order. This would allow the user to manage memory efficiently on their end. The interface would look something like:

import cc3d
import numpy as np

builder = cc3d.connected_components_builder()
for z in range(128):
     builder.add_z_slice(img[:,:,z])
for z in range(128):
     img[:,:,z] = builder.relabel(img[:,:,z])