Implement splitting long scenes.

[luziferius]

Currently, long scenes cannot be split.

• • Add a CLI argument to limit the scene length. Already done, just un-comment the code block.
• • Implement parsing PTS values based on the codec time base.
• • Split long scenes to keep the length below the given command line argument value.
• • Do something about the last scene, which currently has no known length and can be of arbitrary length. So somehow determine it’s length and split it, if it is longer than the maximum scene length.