Allow entries to be published without any outer feed

entry.go

@@ -249,3 +249,13 @@ func (e *Entry) Check() error {
 
 	return nil
 }
+
+// ToXML converts the Feed to XML. It returns a string and an error.
+func (e *Entry) ToXML(encoding string) (string, error) {
+	xml, err := xml.MarshalIndent(e, "", "  ")
+	if err != nil {
+		return "", fmt.Errorf("error xml encoding entry: %v", err)
+	}
+
+	return fmt.Sprintln(`<?xml version="1.0" encoding="`+encoding+`"?>`) + string(xml), nil
+}