Returns an entity containing other entities. This is a useful way to keep related entities together. They will be drawn in the order they appear in the internal :entities vector. Any keys in the bundle, such as :x and :y, will be passed down to all the internal entities unless they already have those keys.

(bundle (shape :filled) (shape :line))
(assoc (bundle (shape :filled) (shape :line))
       :x 100 :y 100)