Refactor encoding to use *string instead of string as input

I don't want to clone the whole input string

encoding/coder.go

@@ -3,6 +3,6 @@ package encoding
 import "bytes"
 
 type Coder interface {
-	Encode(s string, buf *bytes.Buffer) error
+	Encode(s *string, buf *bytes.Buffer) error
 	Decode(buf *bytes.Buffer) (string, error)
 }