[fix & feature / functional]

Makefile:
	added more variables for Makefile, seperated stable flags and debug flags
	added -pg and -O3 respectively to stable to debug

main.c:
	apparently changes to main.c mentioned in from the previous-previous commit were not commited

engine.c:
	added code to get a list of available modes and add a screen
	added code to free above-mentioned list but it generates a segfault so it's commented

engine.h:
	two new variables in engine_t, SDL_Surface *screen, *textures;
	removed a circulur dependency to engine.c