expose OptionalEncoder&OptionalDecoder; add attachment to Stream&Iterator for customized decoder/encoder

feature_stream.go

@@ -4,15 +4,16 @@ import (
 	"io"
 )
 
-// Stream is a io.Writer like object, with JSON specific write functions.
+// stream is a io.Writer like object, with JSON specific write functions.
 // Error is not returned as return value, but stored as Error member on this stream instance.
 type Stream struct {
-	cfg       *frozenConfig
-	out       io.Writer
-	buf       []byte
-	n         int
-	Error     error
-	indention int
+	cfg        *frozenConfig
+	out        io.Writer
+	buf        []byte
+	n          int
+	Error      error
+	indention  int
+	Attachment interface{} // open for customized encoder
 }
 
 // NewStream create new stream instance.