💥 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/lang/web/+css.el

@@ -24,7 +24,8 @@
 ;;
 ;;; Major modes
 
-(add-hook! (css-mode sass-mode stylus-mode) #'rainbow-mode)
+(add-hook! '(css-mode-hook sass-mode-hook stylus-mode-hook)
+           #'rainbow-mode)
 
 ;; built-in, and contains both css-mode & scss-mode
 (after! css-mode
@@ -47,7 +48,8 @@
 ;;; Tools
 
 (when (featurep! +lsp)
-  (add-hook! (css-mode sass-mode less-css-mode) #'lsp!))
+  (add-hook! '(css-mode-hook sass-mode-hook less-css-mode-hook)
+             #'lsp!))
 
 
 (use-package! counsel-css