function min(out, a, b) {
  out[0] = Math.min(a[0], b[0]);
  out[1] = Math.min(a[1], b[1]);
  return out;
}
Returns the minimum of two vec2's

@param {vec2} out the receiving vector
@param {vec2} a the first operand
@param {vec2} b the second operand
@returns {vec2} out