Attribute suppport

This pull request adds support for XML attributes

Example XML:
```xml
<book author="Test">Book #1</book>
```

Example PHP:
```php
$book= $address->next(new CreationOf('util.address.unittest.Book', [
  '.'       => function($it) { $this->name= $it->next(); },
  '@author' => function($it) { $this->author= new Author($it->next()); }
]);
```