Added delta_yolo_box_accumulate(). Added iou_thresh=0.213 parameter to [yolo] layer IoU(anchor,truth).

include/darknet.h

@@ -280,6 +280,7 @@ struct layer {
     int random;
     float ignore_thresh;
     float truth_thresh;
+    float iou_thresh;
     float thresh;
     float focus;
     int classfix;