Take n elements from the end of the vector v and return both the shorten vector v and the n elements in a separate vector w.
If v has less elements than n, the shorten vector v should be empty and all elements should exist in w.
v = 1:10 [v, w] = pop(v, 3);
v = 1:7 w = 8:10
v = [1; 2; 3] [v, w] = pop(v, 5);
v =  w = [1; 2; 3]