function scale(out, a, b) {
  out[0] = a[0] * b;
  out[1] = a[1] * b;
  return out;
}
Scales a vec2 by a scalar number

@param {vec2} out the receiving vector
@param {vec2} a the vector to scale
@param {Number} b amount to scale the vector by
@returns {vec2} out