Added get_next_sibling and get_previous_siblings
Added get_root method
Added second tree to tests
Added get_siblings method
Added is_child_node method
Added is_descendant_of method
Added is_ancestor_of method
Added get_family method
Added get_leafs method
Refactorized into multiple modules
Better tox.ini setup for flake8
Added MPTTQuerySet with first get_root_node method
Simplified test setup
Added get_root_nodes method