Release 0.11.5

Shadow map filtering

Implement the following shadow map filters:
- Percentage-closer filtering
- Variance shadow map
Improve shadow biasing system. Add normal biasing and far plane bias scaling for directional shadow.
Refactor shadow map filter selection in the scene pipeline. Different shadow map filters take different initialisation parameters.
Add a new argument to addDepthConfiguration for opaque object, the new argument takes a pointer to depth fragment shader. This function will be called by the scene pipeline automatically.
Introduce cross-cascade blending which resolves an ugly line when applying shadow filters at the cascade border. To resolve light bleeding introduced by the blending system, cascade plane can be biased when initialising STPCascadedShadowMap, this bias value is called CascadeBandRadius.
Fine-tune some shadow settings in the demo program to make it looks better.

Remove virtual declaration on the destructor on STPCascadedShadowMap because this class is no longer intended to be a base class.
Simplify cascaded shadow map layer lookup process.
Uniform locations of all light properties are now cached with std::unordered_map using light identifier and light type instead of performing string lookup every time.
STPProgramManager now allows sending uniform data using uniform location.
Add more overloads for setLight() in STPScenePipeline.
Terrain renderer now allows using two different tessellation level of detail controls for normal rendering and depth rendering.
Add support for logarithmic depth buffer, realted settings can be found under STPCameraSetting.

The log depth buffer currently does not work with shadow map because shadow calculations are not in log scale.

Improve error handling for scene pipeline initialisation. Now all values set for the shadow parameters are checked for validity.
Refactor STPDeferredShading.glsl to make it more organised.
Force the shadow map to be a square texture. The resolution of all shadow maps is now specified by a single unsigned integer, namely extent length.

Fix a bad sampling pattern when performing texture splatting smoothing during terrain rendering, which incorrectly assumes the range of coordinate causing most of the samples biased towards negative axis.
Fix an issue where in the texture management system mipmap is used however only a single level of detail is allocated, causing no mipmap is actually being generated.
- STPTextureDatabase now allows user to specify the number of mipmap level to allocate when creating a new texture group.