Closer to Anime

Add animation support of string and boolean without any API breaking. You just get these 2 types of animation support as bonus.

But the road of better animation support is still not end, I am planning of making the animating support of different types isolated which may lead to a more extendable API.

Also I am considering deprecating Animation class in favor of Timeline. Frame based texture switching can be easily handled by Timeline and can be easily controlled instead of implementing its own similar updating functionality.

As Timeline takes place of all the animation stuff, it'll simplify the design and making of a "Timeline Editor" which has gain really high priority on me. I always spend lots of time doing hand-writing animations, and hope an editor will help.