Added sprite sheet class

two files are required the image and a text file which describes the
images like this (starts from 0, 0 , top left)

http://prntscr.com/5hu4no

auto ssheet = SpriteSheet::getInstance();
ssheet->put("spritesheet.png", "spritesheet.txt");
Sprite sprite(ssheet->get("background_game"));
ssheet->end();