Initial work on keymap transforms for non-standard matrixes.

* Allows "gaps" for keyboards like Kyra.
* Allows keyboards with matrixes that don't map the logical key
  locations to have normal looking keymaps when defined.

app/boards/shields/kyria/keymaps/default/keymap.c

@@ -0,0 +1,34 @@
+
+#include <zmk/keys.h>
+#include <zmk/keymap.h>
+#include <keymap.h>
+
+bool zmk_handle_key_user(struct zmk_key_event *key_event)
+{
+	switch (key_event->key)
+	{
+	case CC_LOWR:
+		if (key_event->pressed)
+		{
+			zmk_keymap_layer_activate(1);
+		}
+		else
+		{
+			zmk_keymap_layer_deactivate(1);
+		}
+
+		return false;
+	case CC_RAIS:
+		if (key_event->pressed)
+		{
+			zmk_keymap_layer_activate(2);
+		}
+		else
+		{
+			zmk_keymap_layer_deactivate(2);
+		}
+		return false;
+	}
+
+	return true;
+};