Add function to create a new ID

id.go

@@ -1,12 +1,21 @@
 package atomfeed
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+
+	"github.com/google/uuid"
+)
 
 type ID struct {
 	*CommonAttributes
 	URI URI `xml:"uri"`
 }
 
+func NewID() *ID {
+	return &ID{URI: URI(fmt.Sprint("urn:uuid:", uuid.New()))}
+}
+
 func (i *ID) Check() error {
 	if i.URI == "" {
 		return errors.New("uri element of id empty")