Added Delete methods for slice elements to common attributes, entry, feed, person and source

person.go

@@ -31,6 +31,17 @@ func (p *Person) AddExtension(e *ExtensionElement) {
 	}
 }
 
+// DeleteExtension deletes the Extension from the Person. It return an error.
+func (p *Person) DeleteExtension(id int) error {
+	length := len(p.Extensions)
+	if id > length {
+		return fmt.Errorf("error deleting extension from person %v: id %v out of range %v", p, id, length)
+	}
+
+	p.Extensions = append(p.Extensions[:id], p.Extensions[id+1:]...)
+	return nil
+}
+
 // Check checks the Person for incompatibilities with RFC4287. It returns an
 // error.
 func (p *Person) Check() error {
@@ -50,11 +61,9 @@ func (p *Person) Check() error {
 		}
 	}
 
-	if p.Extensions != nil {
-		for i, e := range p.Extensions {
-			if err := e.Check(); err != nil {
-				return fmt.Errorf("extension element %v of person %v: %v", i, p, err)
-			}
+	for i, e := range p.Extensions {
+		if err := e.Check(); err != nil {
+			return fmt.Errorf("extension element %v of person %v: %v", i, p, err)
 		}
 	}