Major optimization refactor, across the board

+ enable lexical-scope everywhere (lexical-binding = t): ~5-10% faster
  startup; ~5-20% general boost
+ reduce consing, function calls & garbage collection by preferring
  cl-loop & dolist over lambda closures (for mapc[ar], add-hook, and
  various cl-lib filter/map/reduce functions) -- where possible
+ prefer functions with dedicated opcodes, like assq (see byte-defop's
  in bytecomp.el for more)
+ prefer pcase & cond (faster) over cl-case
+ general refactor for code readability
+ ensure naming & style conventions are adhered to
+ appease byte-compiler by marking unused variables with underscore
+ defer minor mode activation to after-init, emacs-startup or
  window-setup hooks; a customization opportunity for users + ensures
  custom functionality won't interfere with startup.

core/core-ui.el

@@ -1,4 +1,4 @@
-;; core-ui.el --- draw me like one of your French editors
+;; core-ui.el -*- lexical-binding: t; -*-
 
 (defvar doom-ui-fringe-size '4 "Default fringe width")
 
@@ -40,9 +40,6 @@
 
 (fset #'yes-or-no-p #'y-or-n-p) ; y/n instead of yes/no
 
-;; auto-enabled in Emacs 25+; I'd rather enable it manually
-(global-eldoc-mode -1)
-
 ;; show typed keystrokes in minibuffer
 (setq echo-keystrokes 0.02)
 ;; ...but hide them while isearch is active
@@ -94,7 +91,7 @@ local value, whether or not it's permanent-local. Therefore, we cycle
 (setq show-paren-delay 0.1
       show-paren-highlight-openparen t
       show-paren-when-point-inside-paren t)
-(show-paren-mode +1)
+(add-hook 'window-setup-hook #'show-paren-mode)
 
 ;;; More reliable inter-window border
 ;; The native border "consumes" a pixel of the fringe on righter-most splits,
@@ -102,7 +99,7 @@ local value, whether or not it's permanent-local. Therefore, we cycle
 (setq-default window-divider-default-places t
               window-divider-default-bottom-width 1
               window-divider-default-right-width 1)
-(window-divider-mode +1)
+(add-hook 'window-setup-hook #'window-divider-mode)
 
 ;; like diminish, but for major-modes. [pedantry intensifies]
 (defvar doom-ui-mode-names
@@ -122,13 +119,17 @@ mode is detected.")
 ;; Bootstrap
 ;;
 
+;; auto-enabled in Emacs 25+; I'd rather enable it manually
+(global-eldoc-mode -1)
+
+;; draw me like one of your French editors
 (tooltip-mode -1) ; relegate tooltips to echo area only
 (menu-bar-mode -1)
 (when (fboundp 'tool-bar-mode)
   (tool-bar-mode -1))
 (when (display-graphic-p)
   (scroll-bar-mode -1)
-  ;; buffer name  in frame title
+  ;; buffer name in frame title
   (setq-default frame-title-format '("DOOM Emacs"))
   ;; standardize fringe width
   (push (cons 'left-fringe  doom-ui-fringe-size) default-frame-alist)
@@ -191,7 +192,7 @@ file."
       (set-buffer-modified-p nil))
     nil)
 
-  (add-hook! (highlight-indentation-mode highlight-indentation-current-column-mode)
+  (defun doom|init-highlight-indentation ()
     (if (or highlight-indentation-mode highlight-indentation-current-column-mode)
         (progn
           (doom|inject-trailing-whitespace)
@@ -199,7 +200,9 @@ file."
           (add-hook 'after-save-hook #'doom|inject-trailing-whitespace nil t))
       (remove-hook 'before-save-hook #'delete-trailing-whitespace t)
       (remove-hook 'after-save-hook #'doom|inject-trailing-whitespace t)
-      (delete-trailing-whitespace))))
+      (delete-trailing-whitespace)))
+  (add-hook! (highlight-indentation-mode highlight-indentation-current-column-mode)
+    #'doom|init-highlight-indentation))
 
 ;; For modes that don't adequately highlight numbers
 (def-package! highlight-numbers :commands highlight-numbers-mode)
@@ -265,8 +268,8 @@ file."
 ;; indicators for empty lines past EOF
 (def-package! vi-tilde-fringe
   :when (display-graphic-p)
-  :demand t
-  :config (global-vi-tilde-fringe-mode t))
+  :commands global-vi-tilde-fringe-mode
+  :init (add-hook 'window-setup-hook #'global-vi-tilde-fringe-mode))
 
 ;; For a distractions-free-like UI, that dynamically resizes margets and can
 ;; center a buffer.
@@ -292,12 +295,11 @@ file."
              (byte-compile #',sym))))))
 
 (defsubst doom--prepare-modeline-segments (segments)
-  (let (segs)
-    (dolist (seg segments (nreverse segs))
-      (push (if (stringp seg)
-                seg
-              (list (intern (format "doom-modeline-segment--%s" (symbol-name seg)))))
-            segs))))
+  (cl-loop for seg in segments
+           if (stringp seg)
+            collect seg
+           else
+            collect (list (intern (format "doom-modeline-segment--%s" (symbol-name seg))))))
 
 (defmacro def-modeline! (name lhs &optional rhs)
   "Defines a modeline format and byte-compiles it. NAME is a symbol to identify