* clutter/clutter-score.[ch]: Remove all the API changes, and
just add a clutter_score_append_at_marker(); the implementation
remains the same, but the marker must be explicitly created by
the developer. The ids are no longer used to create implicit
markers, so they can return to be unsigned integers.
* clutter/clutter-timeline.[ch]:
(clutter_timeline_has_marker): Add a function to query a timeline
for a marker being set.
* tests/test-score.c (main): Update with the API changes.
* clutter.symbols: Update exported symbols.
* clutter.symbols: Add new symbols
* clutter/clutter-score.[ch]: Use the newly added marker API
on the timelines to implement attaching timelines at specific
points, using either milliseconds or frames.
* tests/test-score.c (main): Test the new API.
* clutter/clutter-score.[ch]: Reimplement ClutterScore using
a N-ary tree to store the timelines. Remove clutter_score_add():
the same functionality can be achieved by passing a NULL
parent to clutter_score_append().
* tests/test-score.c: Update ClutterScore test unit, and add
debug printouts.
