Add instructions to clean contents of build/lib.
Moved "include" statement to beginning of Makefiles.
Add class for quit warning.
Add window class to makefiles.
Add class for loading an SDL_Window & SDL_Renderer.
Clean up for aesthetics.
Change section 5.3.2 name to "GNU make" & add section 5.3.3 "MinGW make".
Add compiling instructions skeleton.
Replace "Makefile" with convenience Makefiles for GNU/Linux & BSD platforms.