SDL_helpers: Remove method SDL_RECT(coords) & add SDL_RECT(pos, size)
shapes/Rectangle: Refactor class to kiss nom::Coords goodbye

* Inherit from Transformable
* Introduce color getter
* Misc renames
examples/app: Use diff fill strat for bottom info_box
Introduce Shape class
Rectangle: Refactor to inherit from nom::Shape
Shape: Split color_ member into two (fill & outline)
Line: Refactor to inherit from nom::Shape
Point: Refactor class to inherit from nom::Shape
GrayFrame: Refactor class to inherit from Transformable
SpriteSheet: Replace Coords w/ IntRect
GrayFrame: Introduce constructor for Point2i, Size2i objects
MessageBox: Refactor class to inherit from Transformable
math/Coords: Removal of deprecated class
Point2, Rect: Introduce binary operator overloads

* Color4, Point2: Clean up copy constructor; use init-list instead of
assignment.

* Color4, Point2..3, Rect: Introduce get method
tests/Makefile: Introduce run target && NOM_DEBUG_TESTS #define
tests/math: Add tests for Point2, Rect operator overloads

* See: do_point2_test(), do_rect_test2(), do_rect_test3()
* Implement dialog message box popup when we fail a test