Mac OS X Notification Center support, for Mountain Lion and higher.

Code relies on AppleScript (osascript) to trigger the notification. I think for Mac it should be considered default for auto detect mode, since growl isn't free and is not installed everywhere.

io_lib:format trickery is to make code with quote double escaping a bit easier to read.

Let me know if this works for you or if I need to make some changes.