Flood, drain, hollow and outline use cartesian neighbors

[Firigion]

Flood, drain, hollow and outline only check for direct cartesian neighbors (the six blocks in the positive and negative offset along the axes). This is fine for most cases, but it produces counter intuitive results in some cases. Particularly in cases where an outline brush is meant to be applied multiple times to give a thicker outline: the second application doesn't work properly, since the outline placed by the app is not considered as a "block of blocks" (they connect only diagonally in some cases).

I think the best solution for this will be adding a new flag that affects all functions that check neighbors, maybe a -n flag? Naming is hard.