Group-based sprite collision tools and sprite collision detection
predicates.

The predicate functions in this namespace apply to sprites if they
are named `<foo>?` and apply to geometric data structures (lines,
rectangles, polygons etc.) if they are names `<foo>?*`. 

These side-effecting functions draw various shapes to the game
window.

Positions (`pos`) are `[x y]` vectors, so are
dimensions (`size`).

Polygons (`poly`) are a vector of `[x y]` point vectors which are
relative to the `pos`.

Colors are `[r g b a]` vectors.

Tween library for interpolating game object properties between
absolute or relative values.

Comprehensive easing functions for different interpolation curves.