Add BinlogEvent.ByteLen func

Author: Dylan Terry

replication/event.go

@@ -38,6 +38,10 @@ func (e *BinlogEvent) Dump(w io.Writer) {
 	e.Event.Dump(w)
 }
 
+func (e *BinlogEvent) ByteLen() int {
+    return len(e.RawData)
+}
+
 type Event interface {
 	// Dump Event, format like python-mysql-replication
 	Dump(w io.Writer)