aqhome: make datafile a virtual class. Add datafile_direct.

this is to allow for cached data file handling later.

aqhome/data/datafile_direct.h

@@ -0,0 +1,26 @@
+/****************************************************************************
+ * This file is part of the project Gwenhywfar.
+ * Gwenhywfar (c) by 2023 Martin Preuss, all rights reserved.
+ *
+ * The license for this file can be found in the file COPYING which you
+ * should have received along with this file.
+ ****************************************************************************/
+
+#ifndef AQH_DATAFILE_H
+#define AQH_DATAFILE_H
+
+
+#include "aqhome/data/storage.h"
+#include "aqhome/data/datafile.h"
+
+#include <gwenhywfar/list.h>
+
+
+AQHOME_API AQH_DATAFILE *AQH_DataFileDirect_new(const char *fileName, uint64_t valueId);
+
+AQHOME_API const char *AQH_DataFileDirect_GetFileName(const AQH_DATAFILE *df);
+
+
+#endif
+
+