Cel shader and outline shader implementation.

Reference:

1. Unity-chan toon shading techniques.(https://twitter.com/i/moments/781667626942603265)
2. Borderlands implementation of sobel depth shader.
3. Manifold Garden's edge detection shader (http://williamchyr.com/2015/08/edge-detection-shader-deep-dive-part-1-even-or-thinner-edges/)

Skybox and deffered rendering followed the tutorials for Unity shader basics. Tutorials from zhihu https://zhuanlan.zhihu.com/p/43588045 （跟着教程实现Unity天空盒和延迟渲染着色器，内容来自知乎https://zhuanlan.zhihu.com/p/43588045)

Also implemented some random tutorials based on mood. （看心情实现一些教程上的shader<或者模仿>）