On iOS, only compile IOSurface support, and link IOSurface framework to
libMoltenVK.dylib, if IPHONEOS_DEPLOYMENT_TARGET is at least iOS 11.0.
Update to latest version of SPIRV-Cross.
Update MoltenVK version to 1.0.15.
via vkGetPipelineCacheData(), vkCreatePipelineCache() & vkMergePipelineCaches().
Add the cereal serialization framework as a dependency.
Update documentation. Update project settings to Xcode 9.3.