Some cleanup
Added comment explaining dnf structure
Better support for tuples in extra params in @cached and jinja2 decorators
Made default file cache dir more specific
Support @cached_as(SomeModel)
Support for flex models

Strange things in QuerySet structure should provide __uniq_key__().
Attributes of model now accessed with getattr() and can be abstracted better
than when cacheops was using __dict__.
Updated CHANGELOG