[Keyboard] XD75 refactor (#5420)

* Refactor layout macro names

Update the names of the layout macros to reflect QMK's desired usage.

- KEYMAP renamed to LAYOUT
  - colinta keymap updated accordingly
- KC_KEYMAP renamed to LAYOUT_kc
  - mtdjr keymap updated accordingly

* Update xd75.h to use #pragma once include guard

* Update keymaps to use QMK_KEYBOARD_H

* Refactor default keymap

- updated to use layout macro
- remove deprecated action_get_macro function
- add functions from QMK keymap.c template
  - process_record_user
  - matrix_init_user
  - matrix_scan_user
  - led_set_user

* Update supporting files

- updated config.h files to use #pragma once include guard
- remove errant QUANTUM_DIR code block

* Rename readme files to fully lowercase filenames

* Restructure keyboard readme

Updated the readme to better align with the current QMK template.

* Bugfixes to supporting files

keyboards/xd75/keymaps/cbbrowne/rules.mk

@@ -1,5 +1,5 @@
 # Build Options
-#   change to "no" to disable the options, or define them in the Makefile in 
+#   change to "no" to disable the options, or define them in the Makefile in
 #   the appropriate keymap folder that will get included automatically
 #
 BOOTMAGIC_ENABLE = no       # Virtual DIP switch configuration(+1000)
@@ -18,7 +18,3 @@ API_SYSEX_ENABLE = no      # Enable SYSEX API (+5390)
 
 # Do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
 SLEEP_LED_ENABLE = no    # Breathing sleep LED during USB suspend
-
-ifndef QUANTUM_DIR
-	include ../../../../Makefile
-endif