Added and corrected comments

logo.go

@@ -12,10 +12,13 @@ type Logo struct {
 	URI IRI `xml:"uri"`
 }
 
+// NewLogo creates a new Logo. It returns a *Logo.
 func NewLogo() *Logo {
 	return &Logo{URI: IRI(fmt.Sprint("urn:uuid:", uuid.New()))}
 }
 
+// Check checks the Logo for incompatibilities with RFC4287. It returns an
+// error.
 func (l *Logo) Check() error {
 	if l.URI == "" {
 		return errors.New("uri element of logo empty")