add GameWindow::close()
add GameWindow::close()

bvssvni/piston,axelmagn/piston,bvssvni/piston,KevinFrans3/piston,Potpourri/piston,oldmanmike/piston,PistonDevelopers/piston,caldwell/piston,tempbottle/piston,placrosse/piston,PistonDevelopers/piston,mitchmindtree/piston,getynge/piston