A Clutter::Score allows you to start and stop several timelines at
once, or run them in sequence one after the other.
To add a timeline that should start first, call Clutter::Score::append()
without the parent argument. All such timelines will be started when you call
Clutter::Score::start().
To add a timeline that should be started when a previously added timeline stops, call
Clutter::Score::append() with the first timeline for the
parent argument.