Add unit testing

[JakeWharton]

It would be beneficial to include small (<1s) movie samples (read-only) which would be duplicated and then run the script on it. Multiple passes would be needed to test out each of the main features. The outputs of mkvinfo and mkvmerge -i could be used to ensure a proper output. This will greatly help development of future versions since we (the developers) don't even use the script anymore.