Full factorial

This script is similar to fullfact, however instead of number of levels, value of levels are required as input
usage: des_mat = full_fact([-1 1],[100 200 300],[1:4]);

arguments: (input)
x1,x2, x3- variable levels either in row or column vector. These are
not number of levels but the levels itself

arguments: (output)
des_mat - mxn m= total number of designs (product of all levels) and
n is number of variables
The first column shows all the first variable levels, second
column shows second variable levels and so on.

Example usage:
x1=[-1 1];x2=[100:100:300];
des_mat = full_fact(x1,x2) % OR
des_mat = full_fact([-1 1],[100:100:300])
des_mat =
-1 100
-1 200
-1 300
1 100
1 200
1 300