move encoders out to plugins

plugins/config/encoder/xml/xml.go

@@ -0,0 +1,25 @@
+package xml
+
+import (
+	"encoding/xml"
+
+	"github.com/micro/go-micro/v2/config/encoder"
+)
+
+type xmlEncoder struct{}
+
+func (x xmlEncoder) Encode(v interface{}) ([]byte, error) {
+	return xml.Marshal(v)
+}
+
+func (x xmlEncoder) Decode(d []byte, v interface{}) error {
+	return xml.Unmarshal(d, v)
+}
+
+func (x xmlEncoder) String() string {
+	return "xml"
+}
+
+func NewEncoder() encoder.Encoder {
+	return xmlEncoder{}
+}