Multiple grouped product items feature

[sekgobela-kevin]

This is related to issue #17 of perock which was not added to prodius.
This issue depends on issue #3 as grouped cartesian product is not yet available in broote.

What needed is to have multiple grouped items alternating each other over waiting for each other.
As already said, this feature may depend on issue #3 which is not yet implemented.

BEFORE:

prodius.product([0,1], [2,3]) -> [(0, 2), [0, 3), (1,2), (1,3)]

AFTER:

prodius.product([2,3], group=[0,1], max_multiple=2) -> [(0, 2), [1, 2), (0,3), (1,3)]

group argument as in #3 causes product results to be grouped but here they are not.
max_multiple argument should create new iterable that flattens everything back normal.

Realise that results are similar but not differ by order.