Fix some memory leaks

src/lisp.c

@@ -52,7 +52,10 @@ void lisp_init(void) {
     lisp_init_stack();
 }
 
-void lisp_shutdown(void) {}
+void lisp_shutdown(void) {
+    lisp_gc_teardown();
+    lisp_teardown_stack();
+}
 
 DEFUN(eval, "eval", (LispVal * form), "(form)", "") {
     if (!OBJECTP(form)) {