Added a void* user_data parameter to Clipboard function handlers. (#875)

examples/apple_example/imguiex-ios/imgui_impl_ios.mm

@@ -3,6 +3,9 @@
 // Providing a standalone iOS application with Synergy integration makes this sample more verbose than others. It also hasn't been tested as much.
 // Refer to other examples to get an easier understanding of how to integrate ImGui into your existing application.
 
+// TODO:
+// - Clipboard is not supported.
+
 #import <OpenGLES/ES3/gl.h>
 #import <OpenGLES/ES3/glext.h>
 
@@ -288,7 +291,6 @@ void ImGui_ClipboardCallback(uSynergyCookie cookie, enum uSynergyClipboardFormat
     printf("Synergy: clipboard callback TODO\n" );
 }
 
-
 @interface ImGuiHelper ()
 {
     BOOL _mouseDown;