Added quantify() from itertools recipes via Kayla's PR.
Initial implementation of iroundrobin().

Not quite finished. Need to implement `take()` before the unit tests
become meaningful.
Implemented take() from itertools recipes.

Test failing because of `ichain()` issue in `take()` test?
Updated roundrobin() to pass tests.
Ported itabulate() from itertools recipes via Kayla's PR.