Reference to boxes

Modules in the library:

• boxes — convenience reexports.
• boxes.box — contains the Box class and the context() function.
• boxes.cartesian — contains the Vect and Rect classes.
• boxes.constrain — a collection of constraints.
• boxes.display — render some boxes to an image file.
• boxes.context — contains the Context class which holds the equations constraining a set of boxes.