Added Point and Size classes to replace Rectangle when it is overkill.
Point/Size interface for Rectangle (there will a ridiculous amount of get_xy for some time now).
Added missing forward declarations of Point and Size.
Video and VideoMode now use Size instead of Rectangle to represent sizes.
Surface::create now takes a Size instead of a Rectangle.
Used Size instead of Rectangle when meaningful in Sprite, SpriteAnimationDirection and SpriteAnimationSet.
Used Size objects instead of Rectangle to represent sizes in Grid.
Map::get_size now return a Size instead of a Rectangle.
MapEntity::get_size returns Size instead of Rectangle.
TextSurface::get_size returns Size instead of Rectangle.
Replaced unneeded Rectangle instances by Size instances.
DialogBoxSystem::text_position went from Rectangle to Point.
Drawable::xy went from Rectangle to Point.
Fixed incorrect signatures for operator+ and operator-.
Turned a bunch of Rectangle into Point when they were overkill.
StraightMovement::initial_xy went from Rectangle to Point.
Geometry module works with points instead of rectangles.
SpriteAnimationDirection::origin went from Rectangle to Point.
Block's initial_position and last_position are now points.
Crystal::star_xy went from Rectangle to Point.