[major - unfunctional] organised files, i.e. separated code

added:
	src/GameEngine.{cpp,hpp}
	src/loop.cpp
	src/physics.cpp
	src/render.cpp
	src/pool.hpp

main.cpp:
	is now a husk, makes a GameEngine and starts the loop() function
	use later to initialise other components, like networking, GUIs

src/pool.hpp:
	apparently, you can't separate class declarations and functions into different files when you use templates..