Ex 8 - 11
Ex 12: fibs, from, constant, ones via unfold
Terminate unfold on nil
Ex 13 - map_via_unfold

I also had to fix the termination condition in unfold.  It terminates on nil not {nil, _}.
Ex 13: take using unfold
Ex13: take_while using unfold
Ex 13: zip
Ex 13: zip_all
Ex 14 starts_with
Ex 15: tails
Ex 16: scan
Update for Elixir 0.15