Replaced NSLog with DLog for debug only logging

- If you want to enable debug logging, you need to follow this step:
  "Right-click on your target and click Get Info. Select the Build tab.
  Make sure Configuration is set to Debug. Add -DDEBUG to the Other C
  Flags of your target."
- See: http://www.cimgf.com/2009/01/24/dropping-nslog-in-release-builds/
- Fixes #45