added customizable options
added customizable options

VANITAX/PhysicsJS,jpellerin/PhysicsJS,mcanthony/PhysicsJS,griever989/PhysicsJS,pietro909/PhysicsJS,rohit765/PhysicsJS,eric-seekas/PhysicsJS,haithemaraissia/PhysicsJS,Nayar/PhysicsJS,mcanthony/PhysicsJS,pietro909/PhysicsJS,rohit765/PhysicsJS,Nayar/PhysicsJS,Luwdo/PhysicsJS,Rawneed/PhysicsJS,Luwdo/PhysicsJS,wellcaffeinated/PhysicsJS,VANITAX/PhysicsJS,griever989/PhysicsJS,wellcaffeinated/PhysicsJS,eric-seekas/PhysicsJS,Rawneed/PhysicsJS,jpellerin/PhysicsJS,haithemaraissia/PhysicsJS