Modified the Scene and Geometry.
Add the implement of trace_pixel in Raytracer.
Modified soft shadow. Finished shade.
Added hit function to Sphere class.
Added triangle interpolation to triangle class and operators to material class.
Added hit function to Triangle class.
Added hit to Model and Mesh. Changed Material.
Finished basic ray tracing. Started debugging.
Debugging shadow with test.scene.
Fixed shadows' bug. Added mirror reflection.