Instanciate common attributes everywhere so one can simply use the extend method

date.go

@@ -18,7 +18,10 @@ func DateTime(t time.Time) string {
 
 // NewDate creates a new Date. It returns a *Date.
 func NewDate(t time.Time) *Date {
-	return &Date{DateTime: DateTime(t)}
+	return &Date{
+		CommonAttributes: newCommonAttributes(),
+		DateTime:         DateTime(t),
+	}
 }
 
 // Check checks the Date for incompatibilities with RFC4287. It returns an