Add tutorial 18

18_keyStates/LButton.c
18_keyStates/LButton.h
18_keyStates/LTexture.c
18_keyStates/LTexture.h
18_keyStates/LTexture.o
18_keyStates/Makefile
18_keyStates/README.md
18_keyStates/common.c
18_keyStates/common.h
18_keyStates/common.o
18_keyStates/down.png
18_keyStates/keystates.c
18_keyStates/keystates.o
18_keyStates/keystates.out
18_keyStates/left.png
18_keyStates/press.png
18_keyStates/right.png
18_keyStates/up.png