[Keymap] Added HHKB Keymap and user config (#8119)

* Added my config

* Update my keymap

* Improve quality of brett.c

* Finish cleaning brett.c

* Remove QMK_FIRMWARE_H

* Update keyboards/hhkb/keymaps/brett/keymap.c

Co-Authored-By: Ryan <fauxpark@gmail.com>

Co-authored-by: Ryan <fauxpark@gmail.com>

users/brett/brett.h

@@ -0,0 +1,25 @@
+#pragma once
+
+enum userspace_custom_keycodes {
+  PLACEHOLDER = SAFE_RANGE, // Can always be here
+  FAT_ARROW, // =>
+  SKINNY_ARROW, // ->
+  REVERSE_ARROW, // <-
+  CONCAT, // <>
+  MAP, // <$>
+  MAP_FLIPPED, // <#>
+  FLAP, // <@>
+  PIPE, // |>
+  ALT, // <|>
+  APPLY, // <*>
+  AND, // &&
+  OR, // ||
+  BIND, // >>=
+  BIND_FLIPPED, // =<<
+  VOID_LEFT, // <$
+  VOID_RIGHT, // $>
+  DOUBLE_COLON, // ::
+  FLASH // Handle keyboard flashing
+};
+
+bool process_record_keymap(uint16_t keycode, keyrecord_t *record);