new: dict directory (#27)

* new: `dict` directory

* cleanup

Author: aMahanna

nx_arangodb/classes/dict/__init__.py

@@ -0,0 +1,8 @@
+from .adj import (  # noqa
+    adjlist_inner_dict_factory,
+    adjlist_outer_dict_factory,
+    edge_attr_dict_factory,
+    edge_key_dict_factory,
+)
+from .graph import graph_attr_dict_factory, graph_dict_factory  # noqa
+from .node import node_attr_dict_factory, node_dict_factory  # noqa