bugfix: Top.path was returning None, Top.category is an int
raise StopIteration when no more items are found on page

for...else clausules aren't executed when the for is empty but when it
finished without a break. This way, we check for the first element,
raise StopIteration if not present, yield the first element and then all
the rest otherwise
make Paginated.next() return itself and define Paginated.previous()