0.1

* Description:  1. Naively split "render" into 8 threads
*     2. Reduce huge overhead due to call by value
*     3. Reduce the number of multiplication when counting a, b, c, d in
"ray_sphere".
*
* Issue:   1. "ray_sphere" is the hottest function
*     2. Write inline assembly to speed up counting a, b, c, d.