nc:`itertools.tee` is used to cache
    elements as necessary.

    >>> from itertools import count
    >>> all_chunks = ichunked(count(), 4)
    >>> c_1, c_2, c_3 = next(all_chunks), next(all_chunks), next(all_chunks)
    >>> list(c_2)  # c_1's elements have been cached; c_3's haven't been
    [4, 5, 6, 7]
    >>> list(c_1)
    [0, 1, 2, 3]
    >>> list(c_3)
    [8, 9, 10, 11]

    N)