checkers/spell: fix z=, zq, zw & personal dictionary

+ Fixes ispell not noticing allowed words in your personal dictionary.
  So +spell/correct would sometimes correct words that spell-fu wasn't
  highlighting as incorrect, and sometimes wouldn't correct words that
  were.
+ Fixes spell-fu refusing to read or write to the personal dictionary if
  the file didn't already exist beforehand (for zq and zw).
+ Change ispell-dictionary fallback from "en_US" (which aspell won't
  always recognize) to "en".
+ Moved ispell-personal-dictionary to ~/.emacs.d/.local/etc/ispell/ by
  default.

modules/checkers/spell/autoload.el

@@ -49,6 +49,15 @@
 (defun +spell/correct ()
   "Correct spelling of word at point."
   (interactive)
+  ;; We fake awareness for our personal dictionary by stopping short if spell-fu
+  ;; hasn't highlighted the current word. This is necessary because
+  ;; ispell/aspell struggles to find our `ispell-personal-dictionary' if it's
+  ;; not in $HOME.
+  (unless (memq 'spell-fu-incorrect-face (face-at-point nil t))
+    (user-error "%S is correct" (thing-at-point 'word t)))
+  (ispell-set-spellchecker-params)
+  (save-current-buffer
+    (ispell-accept-buffer-local-defs))
   (if (not (or (featurep! :completion ivy)
                (featurep! :completion helm)))
       (call-interactively #'ispell-word)