cmake SPNG examples

facebookresearch/habitat-sim src/cmake/FindMagnumPlugins.cmake :635 

find_package(Spng REQUIRED)

Warzone2100/warzone2100 lib/ivis_opengl/CMakeLists.txt :72 

find_package(SPNG CONFIG REQUIRED)

mosra/magnum-plugins modules/FindMagnumPlugins.cmake :656 

find_package(Spng REQUIRED)