Updated the iOS Objective-C code to use NSDictionary/NSArray/NSNumber literals and subscripting, for improved code clarity.

This requires at least Xcode 4.5 and the iOS 6 SDK to build, but it doesn't change the minimum supported runtime version (iOS 5.1). Less than 2% of iOS users are running iOS 5, so I hope developers aren't trying to build SDL using an SDK which doesn't support iOS 6/7...

src/video/uikit/SDL_uikitopenglview.m

@@ -94,10 +94,10 @@
         CAEAGLLayer *eaglLayer = (CAEAGLLayer *)self.layer;
 
         eaglLayer.opaque = YES;
-        eaglLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
-                                        [NSNumber numberWithBool: retained], kEAGLDrawablePropertyRetainedBacking,
-                                        colorFormat, kEAGLDrawablePropertyColorFormat,
-                                        nil];
+        eaglLayer.drawableProperties = @{
+            kEAGLDrawablePropertyRetainedBacking: @(retained),
+            kEAGLDrawablePropertyColorFormat: colorFormat
+        };
 
         /* Set the appropriate scale (for retina display support) */
         self.contentScaleFactor = scale;