(insert! deq idx ..args)
  deq: a deque
  idx: an int
  args: zero or more arguments (any type)
  returns any type

Inserts one or more elements into a deque.

The index can be negative, or just past the end of the deque. The left-most inserted element will have the index idx.

(let ar (arr 'a 'b 'c))
(insert! ar 1 'x 'y)
(prn ar) ; prints (a x y b c)
(insert! ar 5 'd)
(prn ar) ; prints (a x y b c d)