Add resizing processor to example

Demo/Demo/Kingfisher-Demo/ViewControllers/ProcessorCollectionViewController.swift

@@ -39,6 +39,7 @@ class ProcessorCollectionViewController: UICollectionViewController {
     
     var processors: [(ImageProcessor, String)] = [
         (DefaultImageProcessor.default, "Default"),
+        (ResizingImageProcessor(referenceSize: .zero), "Resizing"),
         (RoundCornerImageProcessor(cornerRadius: 20), "Round Corner"),
         (RoundCornerImageProcessor(cornerRadius: 20, roundingCorners: [.topLeft, .bottomRight]), "Round Corner Partial"),
         (BlendImageProcessor(blendMode: .lighten, alpha: 1.0, backgroundColor: .red), "Blend"),