Some code cleaning.
Create simple functions for neighborhood finding
 neigh2,
 neigh4 (doesn't provide good results)
 cost (compute the entropy of position, 0 if position is empty)
simple MAP estimation of the grid.
see Grid.map_estimation and Grid.map_energy

reach 512
current problem: too many labels with small number.
map estimation
keeps a relatively small number of labels on the grid
0,0 is usually the max
not excellent so far