Created ag-chart-error-quark and AgChartError enum

src/ag-chart.h

@@ -6,6 +6,11 @@
 
 G_BEGIN_DECLS
 
+typedef enum {
+    AG_CHART_ERROR_LIBXML,
+    AG_CHART_ERROR_CORRUPT_FILE,
+} AgChartError;
+
 #define AG_TYPE_CHART         (ag_chart_get_type())
 #define AG_CHART(o)           (G_TYPE_CHECK_INSTANCE_CAST((o), AG_TYPE_CHART, AgChart))
 #define AG_CHART_CLASS(k)     (G_TYPE_CHECK_CLASS_CAST((k), AG_TYPE_CHART, AgChartClass))
@@ -39,6 +44,9 @@ gchar *ag_chart_get_country(AgChart *chart);
 void ag_chart_set_city(AgChart *chart, const gchar *city);
 gchar *ag_chart_get_city(AgChart *chart);
 
+#define AG_CHART_ERROR (ag_chart_error_quark())
+GQuark ag_chart_error_quark(void);
+
 G_END_DECLS
 
 #endif /* __AG_CHART_H__ */