Make that QXlsx::Document is the only subclass of QObject

src/xlsx/xlsxdocument_p.h

@@ -22,7 +22,7 @@ public:
     QString packageName; //name of the .xlsx file
 
     QMap<QString, QString> documentProperties; //core, app and custom properties
-    Workbook *workbook;
+    QSharedPointer<Workbook> workbook;
 };
 
 }