Make lighting more realistic

[zhengyangxia]

Perhaps a main light source from the Sun and a supplemental parallel light.

[xuxiaoqiao]

Current progress:

• [x] Setup base code for post processing
• [x] Support HDR and some sort of tone mapping
• [x] Support blooming
• [ ] tweak gaussian blur radius to improve graphics
• [x] Adjust OpenGL lighting position.
• [ ] tweak the color of the sun