add join function to stdlib

Signed-off-by: Ava Affine <ava@sunnypup.io>

Writing.org

@@ -103,7 +103,7 @@ After the variable declaration list, the next form is one or more unevaluated tr
 #+BEGIN_SRC lisp
   ;; Example let statement accepts one incoming connection on a socket and sends one response
   (let ((conn (accept-conn listen-socket))                      ;; start the var decl list, decl first var
-        (hello-pfx "hello from ")                               ;; start the var decl list, declare second var
+        (hello-pfx "hello from ")                               ;; declare second var
         (hello-msg (concat hello-pfx (get-server-name)))        ;; declare third var from the second var
         (hello-response (make-http-response 200 hello-msg)))    ;; declare fourth var from the third, end list
     (log (concat "response to " (get-dst conn) ": " hello-msg)) ;; evaluates a function call using data from the first and third vars