Introduce mapSDL_Color function & Vector2d typedef, helper funcs for maths
Introduce rescaling algorithm method (low quality); Canvas::init method
Revert "Remove Vector4 class"

This reverts commit 47bc5fac5c5b8eedeefbdfb06a736a3b54a7cc31.
Revert "Update comments"

This reverts commit f17d375f12416a4075e18ddf64de1617bb203fa6.