* [pornpics] add category and listing extractors
Add support for:
- Category pages like /ass/, /milf/, /blonde/ etc.
- Listing pages like /popular/, /recent/, /rating/, /likes/, /views/, /comments/
Category pages use JSON pagination like tags/search.
Listing pages don't support JSON pagination and use different HTML structure.
* [pornpics] simplify category pattern via class ordering
- Move PornpicsCategoryExtractor after PornpicsListingExtractor
so it acts as catch-all, eliminating need for negative lookahead
- Use list comprehension in PornpicsListingExtractor.galleries()
* update docs/supportedsites
