Being able to set a marker at a normalized point on a timeline, instead
of using a specific time, is a nice fit with the current Timeline class
API.
https://bugzilla.gnome.org/show_bug.cgi?id=694319
It's the conformance test suite: there's no need to namespace the files,
just like there's no need to namespace the units.
This commit does not change the Cogl tests: they will be moved to Cogl
over time, and it's easier to do if we leave them as they are.