Added get_queryset_ancestors manager method
Added some documentation
Removed my modifications to README.
Added "include_self" option to get_queryset_ancestors (it was mistakenly
left out.)
* ``get_queryset_ancestors()`` now uses only two database queries.
* Duplicate code that would have existed between
``get_queryset_ancestors()`` and ``get_queryset_descendants()`` has
been consolidated in the "private" method, ``_get_queryset_relatives``
* Unit test for ``get_queryset_ancestors()`` has been written; all tests
pass.
Cleaning up comments in get_queryset_ancestors.
Merge pull request #300 from musashiXXX/master

get_queryset_ancestors. Thanks @musashiXXX