Gets a plane's normal from 3 points on that plane.
var point1 = 0 1 0point2 = 1 1 05point3 = 0 1 -2var norm =console // [0, 1, 0]
out = normal(out, point1, point2, point3)
With three points on the same plane, determines the unit normal and stores it in
out [x, y, z].
MIT, see LICENSE.md for details.