Returns the angle between two vectors.
Since: 3.0
Parameters
vt1: vector 1.vt2: vector 2.
Examples
use <angle_between.scad>
assert(angle_between([0, 1], [1, 0]) == 90);
assert(angle_between([0, 1, 0], [1, 0, 0]) == 90);
assert(round(angle_between([1, 1, 0], [1, 1, sqrt(2)])) == 45);