anti-aliasing
Merge branch 'master' of https://github.com/jingjingwang/557-ray

Conflicts:
	src/RayTracer.cpp
first version of acceleration, tried to use command line to test on box_sphere.ray. Use -b to enable acceleration. Speed: 14s/39s
modified anti
Merge branch 'jwang_acceleration' of https://github.com/jingjingwang/557-ray

Conflicts:
	src/RayTracer.cpp
a simple version of SAH
a simple SAH, 10.8s so far on box_sphere.ray
stash
remove debugging
also try cutting on mins, now 9.8s
...
Merge branch 'jwang_cut_on_both_min_and_max' of https://github.com/jingjingwang/557-ray
added slider for anti-aliasing