Introduce autodefs to replace some settings

+ :popup -> set-popup-rule!
+ :popups -> set-popup-rules!
+ :company-backend -> set-company-backend!
+ :evil-state -> set-evil-initial-state!

I am slowly phasing out the setting system (def-setting! and set!),
starting with these.

What are autodefs? These are functions that are always defined, whether
or not their respective modules are enabled. However, when their modules
are disabled, they are replaced with macros that no-op and don't
waste time evaluating their arguments.

The old set! function will still work, for a while.

modules/lang/php/config.el

@@ -3,7 +3,7 @@
 ;; (def-package! hack-mode
 ;;   :mode "\\.hh$"
 ;;   :config
-;;   (set! :company-backend 'hack-mode '(company-capf)))
+;;   (set-company-backend! 'hack-mode '(company-capf)))
 
 
 (def-package! php-mode
@@ -22,7 +22,7 @@
 
   ;; ac-php provides custom autocompletion, php-extras provides autocompletion
   ;; for built-in libraries
-  (set! :company-backend 'php-mode '(company-ac-php-backend php-extras-company))
+  (set-company-backend! 'php-mode '(company-ac-php-backend php-extras-company))
 
   ;; default is 10; this optimizes `smartparens' performance, but limits sp
   ;; pairs to 6 characters.