refactor associations and make bullet more robust
refactor associations and make bullet more robust

jay3126/bullet,dwb/bullet,sideci-sample/sideci-sample-bullet,flyerhzm/bullet,dwb/bullet,theass/bullet,yakovenkodenis/bullet,danp60/bullet,theass/bullet,rstacruz/bullet,hannahbot/bullet,hannahbot/bullet,0xCCD/bullet,yakovenkodenis/bullet,rrosenblum/bullet,flyerhzm/bullet,sho-h/brakefast,eileencodes/bullet,rstacruz/bullet,PikachuEXE/bullet,flyerhzm/bullet,danp60/bullet,PikachuEXE/bullet,sideci-sample/sideci-sample-bullet,sho-h/brakefast,jay3126/bullet,rrosenblum/bullet,eileencodes/bullet