Improve Precision

Release 0.14.5

Reversed depth buffer (#45)

• Modify projection matrices for main camera and shadow camera to use zero-to-one convention.
• Change clip volume to DirectX convention.
• Flip near and far plane for projection.
• Clear depth of main camera and shadow camera to zero, as well as border colours of shadow texture / samplers.
• Use greater than for depth comparison logic.
• Update implementation for depth reconstruction in shader to match up reversed depth logic.
• Modify shadow bias to use addition instead of subtraction on the fragment depth.
• Add a documentation regarding reversed depth buffer as it is not trivial for developers.

General fixes and improvement

• Avoid updating the light direction for directional light (and hence re-render the shadow map) when the sun is invisible (and hence no light).
• Add a few flags to STPLightShadow to allow user to mask out shadow map update.
• STPSun now calculates the initial sun direction at initialisation.
• Clarify some behaviours in STPDirectionalLight.
• Refactor deferred lighting shader, view direction is computed outside the loop to avoid repetitive calculation.
• Make several colour spectrums to use SRGB format.
• Improve the water opacity function to make the edge connecting the terrain smoother.
• Refactor STPFile, STPSmartDeviceMemory and STPHashCombine to use namespace instead of class.
• Improve GL context robustness.
• Enable no error context on release build.
• Disable depth and stencil buffer on default framebuffer.
• Inline definition for STPNullablePrimitive; declare all functions as noexcept.
• Refactor GL objects management class in STPRealism+.
• Do not quote a variable with ${} when using it as an if condition for CMake.
• Improve documentations for sqlite build script.