Game of life live_neighbor_count wrong neighbour index

[tinoism]

The function in live_neighbor_count of Game of life should iterate delta_* from [-1, 0, 1] instead of from [self.height - 1, 0, 1] and [self.width - 1, 0, 1].

[tinoism]

Just realized that it wouldn't compile... Although the intuition about having the negative index is correct, in rust we annotate the negative indices by adding the length of the array. For instance, "negative indexes like -1 and -2 get added to the length of the slice to become real indices, like len - 1 and len - 2" as indicated in this issue.