innerFillet()
Local rule:
Iterate all positions in vG
 If empty position is found (air) :
Find sum of all voxels inside the surrounding sphere with radius R
 If sum is greater than half the maximum :
Create a voxel in the iterating position
Library function:
 The 3D spherical window is not weighted  proper weight values may improve surface quality. C2/C3?
 Needs margins as large as the radius R
Tutorial example:
