Improve plist pp function

The function now advances through the elements in the list with
`forward-sexp` instead of regex, making it more robust. It also
properly handles lists now.

conner.el

@@ -168,13 +168,14 @@ been called.  You can use `plist-get' to fetch data from it.
     (let ((inhibit-message t)
           (message-log-max nil))
       (lisp-data-mode)
-      (insert (pp-to-string plist))
-      (goto-char (point-min))
+      (prin1 plist (current-buffer))
+      (goto-char (1+ (point-min)))
       (dotimes (i (proper-list-p plist))
-        (when (and (cl-evenp i) (not (eq i 0)))
-          (re-search-forward (pp (nth i plist)))
-          (goto-char (match-beginning 0))
+        (when (and (cl-evenp i) (< (1+ i) (1- (proper-list-p plist))))
+          (forward-sexp 2)
           (newline-and-indent)))
+      (goto-char (point-max))
+      (newline-and-indent)
       (buffer-string))))
 
 (defun conner--pp-plist-list (plist-list)