Append an element x to the end of the vector v and return both the extended vector and the new number of its elements. x can be a vector as well.
In cases where v is a row vector and x is a column vector, or vice versa, v should remain a row/column vector. When v is originally empty, it should preserve the dimensions of x.
v = 1:5; [v, n] = push(v, [6;7;8]);
v = 1:8; n = 8;