Refactor out map.el usage

After some profiling, it turns out map-put and map-delete are 5-7x
slower (more on Emacs 25) than delq, setf/alist-get and add-to-list for
small lists (under 250 items), which is exactly how I've been using
them.

The only caveat is alist-get's signature is different on Emacs 25, thus
a polyfill is necessary in core-lib.

modules/lang/data/config.el

@@ -1,10 +1,10 @@
 ;;; lang/data/config.el -*- lexical-binding: t; -*-
 
 ;; Built in plugins
-(dolist (spec '(("/sxhkdrc\\'" . conf-mode)
-                ("\\.\\(?:hex\\|nes\\)\\'" . hexl-mode)
-                ("\\.plist\\'" . nxml-mode)))
-  (map-put auto-mode-alist (car spec) (cdr spec)))
+(unless after-init-time
+  (push '("/sxhkdrc\\'" . conf-mode) auto-mode-alist)
+  (push '("\\.\\(?:hex\\|nes\\)\\'" . hexl-mode) auto-mode-alist)
+  (push '("\\.plist\\'" . nxml-mode) auto-mode-alist))
 
 (after! nxml-mode
   (set-company-backend! 'nxml-mode '(company-nxml company-yasnippet)))