dot the system directory to hide it from iTunes Sharing

This esssentially hides the retroarch system directory when viewing the
documents directory through iTunes Sharing.

You can't browse folders this way anyways, so having it visible is
essentially useless anyways.

You can of course still get to this directoy via tools like iTools
(non-jailbroken) or ssh'ing into the device (jailbroken).

ios/RetroArch/RetroArch_iOS.m

@@ -53,7 +53,7 @@
 - (void)applicationDidFinishLaunching:(UIApplication *)application
 {
    // TODO: Relocate this!
-   self.system_directory = [NSString stringWithFormat:@"%@/RetroArch", kDOCSFOLDER];
+   self.system_directory = [NSString stringWithFormat:@"%@/.RetroArch", kDOCSFOLDER];
    mkdir([self.system_directory UTF8String], 0755);
          
    // Setup window