Finished light propagation volumes and added documentation.

res/dpr/utility/indirect_library.glsl

res/dpr/utility/indirect_propagation.comp

res/dpr/utility/light_library.glsl

src/scene.hpp

src/strategy/multi_view_stereo.cpp

src/strategy/multi_view_stereo.hpp

src/strategy/native_stereo_deferred.cpp

src/strategy/native_stereo_deferred.hpp

src/strategy/native_stereo_forward.cpp

src/strategy/native_stereo_forward.hpp

src/utility/geometry_buffer.cpp

src/utility/geometry_buffer.hpp

src/utility/indirect_cache.cpp

src/utility/indirect_cache.hpp

src/utility/shadow_cache.hpp

src/vr_application.cpp

src/vr_application.hpp