ARC

While dumping an archive with **PlistExplorer**, I stumbled on a crash. Enabling zombies revealed that it was a memory management related bug. So instead of trying to find the error, I just enabled ARC on the project and sure enough, the crash disappeared!

I also did some minor formatting: using a `@property` where appropriate and moving ivars inside `@implementation`.

Finally, I also inverted the exit status to be consistant with other Unix command line tools.