Programmatically create APNG files
// By Heber Sheffield
public class func save(animatedImageSequence images: Array<CGImage>, withFrameDelay delay: CGFloat, numberOfLoops: Int, to url: URL) {
let fileProperties = [kCGImagePropertyPNGDictionary as String: [kCGImagePropertyAPNGLoopCount as String: numberOfLoops]]
let frameProperties = [kCGImagePropertyPNGDictionary as String: [kCGImagePropertyAPNGDelayTime as String: delay]]
guard let destination = CGImageDestinationCreateWithURL(url, kUTTypePNG, images.count, nil) else { fatalError("couldn't create image destination for url: \(url)") }
CGImageDestinationSetProperties(destination, fileProperties)
for image in images {
CGImageDestinationAddImage(destination, image, frameProperties)
}
CGImageDestinationFinalize(destination)
}