Rewrite :defer semantics

:defer now supports a hook, a cons cell with (SYMBOL . INTEGER) where
SYMBOL is a hook and INTEGER is a number of idle seconds before the
package is autoloaded, or just the integer (as per the default behavior
of :defer).

Also fixes an issue where switch-buffer-deffered packages (like
smartparens) wouldn't load.

core/core-ui.el

@@ -281,13 +281,13 @@ DEFAULT is non-nil, set the default mode-line for all buffers."
 
 ;; undo/redo changes to Emacs' window layout
 (def-package! winner
-  :defer buffer
+  :defer doom-after-switch-buffer-hook
   :preface (defvar winner-dont-bind-my-keys t) ; I'll bind keys myself
   :config (winner-mode +1))
 
 ;; highlight matching delimiters
 (def-package! paren
-  :defer input
+  :defer pre-command-hook
   :config
   (setq show-paren-delay 0.1
         show-paren-highlight-openparen t