Add a "warping mode"

[pinpox]

At the moment the cells outside the grid are assumend to be "dead". A different approach would be to make to grid warp around, meaning: Everything that goes out of the grid at the top, comes back in at the bottom, everything that goes out one side comes back in at the opposite. Another possible option would be to assume the cells outside the border as "alive"

This would need an additional command line parameter to specify the border type:

-b --border [wrap|dead|alive]

The default should be "dead".