Exercise: chunks

Write a generator chunks(items, size): a function with yield that gives out items in chunks — lists of size elements, order kept. items is any iterable: a list, a string, a range or another generator. The last chunk may be shorter.

• list(chunks([1, 2, 3, 4, 5], 2)) → [[1, 2], [3, 4], [5]]
• list(chunks([1, 2, 3], 10)) → [[1, 2, 3]]
• list(chunks("abcde", 3)) → [['a', 'b', 'c'], ['d', 'e']]
• next(chunks([7, 8, 9], 2)) → [7, 8]

Constraints: size is an integer of at least 1; items may be empty, and then the generator gives out no chunks.

Do not add extra imports unless the task says so explicitly.