Merge branch 'functions' of https://github.com/VECcom/Tetris into interface

Conflicts:
	functions.c
Merge branch 'master' of https://github.com/VECcom/Tetris into interface

Conflicts:
	functions.c
added SDL
Merge branch 'functions' of https://github.com/VECcom/Tetris into interface

Conflicts:
	Makefile
	functions.c
	interface.c
	main.c
modified position calculating and added interface option
SDL sometimes caused SIGSEV in glClearColor() and ajusted postion of the field