Append classes found in HTML elements to the list of styles used.
        Because we haven't built the tree, we aren't using the `tag` parameter
        for now.
        @param <string> tag
            The HTML tag we're parsing
        @param <tuple> attrs
            A tuple of HTML element attributes such as 'class', 'id',
            'style', etc. The tuple is of the form ('html_attribute',
            'attr1', 'attr2', 'attr3' ... 'attrN')

def append_styles(self, tag, attrs):
        """
        Append classes found in HTML elements to the list of styles used.
        Because we haven't built the tree, we aren't using the `tag` parameter
        for now.
        @param <string> tag
            The HTML tag we're parsing
        @param <tuple> attrs
            A tuple of HTML element attributes such as 'class', 'id',
            'style', etc. The tuple is of the form ('html_attribute',
            'attr1', 'attr2', 'attr3' ... 'attrN')
        """
        dattrs = dict(attrs)
        if 'class' in dattrs:
            #print "Found classes '%s'" % dattrs['class']
            class_names = dattrs['class'].split()
            dotted_names = map(prepend_dot,class_names)
            dotted_names.sort()
            self.used_classes.extend(' '.join(dotted_names))
            self.unchained_classes.extend(dotted_names)
        if 'id' in dattrs:
            #print "Found id '%s'" % dattrs['id']
            self.used_ids.extend(prepend_hash(dattrs['id'].strip()))