💥 Refactor add-hook! macro & change arg order

This update may potentially break your usage of add-hook! if you pass
the :local or :append properties to it. This is how they used to work:

  (add-hook! :append 'some-mode-hook #'do-something)

Thsoe properties must now follow the hooks, e.g.

  (add-hook! 'some-mode-hook :append #'do-something)

Other changes:
- Various add-hook calls have been renamed to add-hook! because I
  incorrectly assumed `defun` always returned its definition's symbol,
  when in fact, its return value is "undefined" (so sayeth the
  documentation). This should fix #1597.
- This update adds the ability to add multiple functions to hooks
  without a list:

    (add-hook! 'some-mode-hook
               #'do-something
               #'do-something-else)

- The indentation logic has been changed so that consecutive function
  symbols at indented at the same level as the first argument, but forms
  are indent like a defun.

    (add-hook! 'some-mode-hook
               #'do-something
               #'do-something-else)

    (add-hook! 'some-mode-hook
      (message "Hello"))

modules/app/rss/config.el

@@ -36,14 +36,14 @@ easier to scroll through.")
   (make-directory elfeed-db-directory t)
 
   ;; Ensure elfeed buffers are treated as real
-  (add-hook 'doom-real-buffer-functions
+  (add-hook! 'doom-real-buffer-functions
     (defun +rss-buffer-p (buf)
       (string-match-p "^\\*elfeed" (buffer-name buf))))
 
   ;; Enhance readability of a post
   (add-hook 'elfeed-show-mode-hook #'+rss-elfeed-wrap-h)
   (add-hook! 'elfeed-search-mode-hook
-    (add-hook 'kill-buffer-hook #'+rss-cleanup-h nil t))
+    (add-hook 'kill-buffer-hook #'+rss-cleanup-h nil 'local))
 
   ;; Large images are annoying to scroll through, because scrolling follows the
   ;; cursor, so we force shr to insert images in slices.