Add additional link to the document. Links will be embeded only inside of this document.

        >>> add_link(href='styles.css', rel='stylesheet', type='text/css')

def add_link(self, **kwgs):
        """
        Add additional link to the document. Links will be embeded only inside of this document.

        >>> add_link(href='styles.css', rel='stylesheet', type='text/css')
        """
        self.links.append(kwgs)
        if kwgs.get('type') == 'text/javascript':
            if 'scripted' not in self.properties:
                self.properties.append('scripted')