function cross(out, a, b) {
    var ax = a[0], ay = a[1], az = a[2],
        bx = b[0], by = b[1], bz = b[2]

    out[0] = ay * bz - az * by
    out[1] = az * bx - ax * bz
    out[2] = ax * by - ay * bx
    return out
}
Computes the cross product of two vec3's

@param {vec3} out the receiving vector
@param {vec3} a the first operand
@param {vec3} b the second operand
@returns {vec3} out