Combines an array of deques into one deque.
glue is present, all of its elements are inserted between each adjacent pair
glue, and all of the deques in
deqs, must share the same type. For example, if
deqs must be an array of strings.
(let words '("Strike" "the" "Earth!")) (let sentence (join words " ")) (prn sentence) ; prints Strike the Earth!
deqs is empty, returns an empty array (or an empty string if
glue is a string).