Keyboard: 4x4 modular keyboard (#3531)

* add support for 4x4 macropad

* Update readme.md

* set DFU escape key

* cleanup

* Update config.h

* Update keymap.c

* Update config.h

* Update keymap.c

* Update 4x4.h

* reviewed

fudging review automation

* playing with the system

* reverting

* Required additions made

Added support for additional layouts

* tidy up default keymap

keyboards/4x4/4x4.c

@@ -0,0 +1,29 @@
+
+#include "4x4.h"
+
+void matrix_init_kb(void) {
+	// put your keyboard start-up code here
+	// runs once when the firmware starts up
+
+	matrix_init_user();
+}
+
+void matrix_scan_kb(void) {
+	// put your looping keyboard code here
+	// runs every cycle (a lot)
+
+	matrix_scan_user();
+}
+
+bool process_record_kb(uint16_t keycode, keyrecord_t *record) {
+	// put your per-action keyboard code here
+	// runs for every action, just before processing by the firmware
+
+	return process_record_user(keycode, record);
+}
+
+void led_set_kb(uint8_t usb_led) {
+	// put your keyboard LED indicator (ex: Caps Lock LED) toggling code here
+
+	led_set_user(usb_led);
+}