* Add new Cloth NDF
Based on the work by Estevez and Kulla, also known as the "Charlie" sheen.
* Restore DFG computation to GGX
* New proposed approximation for Cloth DFG
* Add "Charlie" cloth DFG approximation to cmgen
* Switch to "Charlie" sheen for cloth shading
* Document the new cloth NDF and DFG approximation
* Fix post-process shader when not in Vulkan
The post-process shader must not flip the source texture when we compile for OpenGL. This happens because we use SPIR-V/Vulkan as an intermediate format.
* Fix the Android build
We need to output a location when targeting SPIR-V for mobile.
