Improvement to Texture System

Release 0.8.13

SuperTest+

• Apply unit and converage testing to STPTextureDefinitionLanguage.
• Apply unit testing to new functions in STPChunk.

STPWorldPipeline

• Major optimisation to STPWorldPipeline. It now caches rendering buffer when the central chunk changes, and only load chunk map from STPChunkStorage and compute splatmap when old chunk map is not available to be reused.
• Type of rendering buffer and cache are all now identified by indices instead of some variable names. This greatly reduced the coding effort such that to update buffers for every type only a single for loop is required.
• Refactor some functions to cutdown line-of-code.

General fixes and improvement

• Removed function getChunkCoordinate() in STPChunk as it is not being used.
• Add a UnuseTextureType identifier in STPTextureFactory for indicating the value when texture type is not used in the texture type dictionary.
  • Also passes this new identifier to the shader and check for unused texture type before searching for texture data in the array.