* clutter/clutter-marshal.list: Add signature for the
::marker-reached signal marshaller.
* clutter/clutter-timeline.[ch]: Add timeline marker API;
using markers it is possible to add a unique identifier to
a particular frame of the timeline, and receive a signal
notification when reaching that particular marker while
playing the timeline. (#641)
* tests/test-timeline.c: Update the test case to check for
the marker-reached signal emission.
* clutter.symbols: Add new symbols.