[mkgmap-dev] New cmdline switch for splitter.jar

Hi Chris, I in fact called it --output-dir initially. However when I first typed it at the commandline, I caught myself writing --destdir. I realized that --destdir is just the name of the option for a lot of tools when specifying a target directory I'm used to. But if you deem --output-dir more accurate, go ahead. It's your code in the end. All the best, /Markus