Class sftools::Locations

It could be interesting to have a Path class and be able to do something like Locations loc; loc.add({"res"}.add({"img"}, {"snd"}), {"extra"}).

It could be usefull to provide a 'combine(LoopFrameStream)' method to use more than one sprite sheet for an animation.

In the same vein a 'add(Frame)' or 'add(begin, end)' could be useful too.

Does 'loop == false' means the animation should keep displaying the last frame or display nothing at all when the last frame is reached ? Currently the first solution is implemented but it might be more cleaver to implement the second one. Or add a LoopPolicy..

Class sftools::Singleton< T, F >

With C++11 we could do even better : by using variadic template we can customize more easily the construction of the unique instance and probably even inherit from T so the singleton object could be used everywhere T is used. However there might be issues with NonCopyable and NonInstanceable.