function scale(out, a, b) {
    out[0] = a[0] * b
    out[1] = a[1] * b
    out[2] = a[2] * b
    return out
}
Scales a vec3 by a scalar number

@param {vec3} out the receiving vector
@param {vec3} a the vector to scale
@param {Number} b amount to scale the vector by
@returns {vec3} out