MInimal working game experience

We've resolved many issues and added a bunch of features, such as levels, collision detection (thanks, @alex-eg), simple interpolated animations, score counting and game over screen.

That work showed us how difficult garbage collecting and message passing is in our system. It took many days to implement things that don't affect gameplay, and they are still working bad.

This release contains poor but working gameplay mechanics. To keep things clean I am reducing scope of milestones to doable within month or two.