GOL-isNeighbor.swift

public func isNeighbor(to cell: Cell) -> Bool {

    let xDelta = abs(self.x - cell.x)
    let yDelta = abs(self.y - cell.y)

    switch (xDelta, yDelta) {
    case (1, 1), (0, 1), (1, 0):
        return true
    default:
        return false
    }

}