Being able to easily set the number of repeats has been a request for
the animation framework for some time now. The usual way to implement
this is: connect to the ::completed signal, use a static counter, and
stop the timeline when the counter hits a specific spot.
In the same light as the :auto-reverse property, we can make it easier
to implement this common functionality by adding a :repeat-count
property that, when set, limits the amount of loops that a Timeline can
perform before stopping itself.
In fact, we can implement the :loop property in terms of the
:repeat-count property just by using a sentinel value mapping to
"infinity", and map loop=FALSE to repeat-count=0, and loop=TRUE to
repeat-count=-1.