math/Point2-inl: Fix a couple missed bugs

* Fix copy constructor's return type
* Fix copy assignment operator
math/Color: Complete conversion to template class

* Introduce two color types (typedefs): Color4u(uint8) & Color4f(float)

* Replace all nom::Color definitions with our new Color4u type across
nomlib; examples, tests & classes.

  SDL_helpers
* Implement SDL_RECT(IntRect) function
* Implement SDL_POINT(Point2i) function
Color: Rename class to Color4
Color: Rename class to Color4
Remove binaries in tests dir
gitignore: Add tests bins to ignore list
Rename of Point2-inl, Point3-inl & Rect-inl

* Removing -inl from each file
Move SDL_helpers source to system dir