Return the (possibly out of bounds) neighbors of a point.

def neighbors((x, y)):
    """Return the (possibly out of bounds) neighbors of a point."""
    yield x + 1, y
    yield x - 1, y
    yield x, y + 1
    yield x, y - 1
    yield x + 1, y + 1
    yield x + 1, y - 1
    yield x - 1, y + 1
    yield x - 1, y - 1