Volume2D Shader version 1.2

• 2021.8.26 Major revision in Volume, delete much redundant code. Make the logic clearer and simpler, more efficient.
• Some bugs are fixed, and the new updates are tested in 4 new maps seen as follows.
  • Able to handle the boundaries which cover more than 360 degs.
  • Able to run in a "Room like" (relatively closed) maps.
  • Better occlusion judgement strategies, less code than before.
  • Four new standard maps are added in the folder maps
  • Mouse control in OpenCV 4, much easier to control your source of light.
  • Notice that if you are looking for a 2D LiDAR simulator, I have built a simple simulator upon this repository, see [Enigmatisms/ParticleFilter], which is awesome.