For example if you are going from tile 1,1 to 1,2 you would get
two notifications if parInclFirst==true, one for 1,1 and one for
1,2. If parInclFirst==false, then you will only get a notification
for 1,2. Note that if the segment passed to to
for_each_voxel_under_segment() is too short and doesn't span over
the initial tile, passing parInclFirst==false will discard the
only callback you would normally get. Effectively this can be used
for a sort of "on tile changed" notification.
