Keyboard: add ergoinu keyboard (#3655)

* add ergoinu

* remove unnecessary code

* replace include guard
delete unused code

* remove unused RGBLED defines

keyboards/ergoinu/split_util.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include <stdbool.h>
+#include "eeconfig.h"
+
+extern volatile bool isLeftHand;
+
+// slave version of matix scan, defined in matrix.c
+void matrix_slave_scan(void);
+
+void split_keyboard_setup(void);
+bool has_usb(void);