issue #28 - plain text/directory listing output on the get CLI

This addresses issue #28 by adding a plain 'directory list' format to the get CLI option.  Here's sample output:

	$ python ~/virtualenvs/ndserviceregistry-venv/bin/ndsr --server '33.33.33.100:2181' --loglevel 50 --recursive --outputformat dir
	/
	/tests
	/tests/locks-45487402d7e545e6a88ef0756c2ccaa4-__lock__
	/tests/locks-272ee302f8624d9b80ef62550a038073
	/tests/locks-e116811a33124ddd8327114e7831c756-__lock__
	/tests/locks-005f17afba1c4fdca30b209cc08c1d9f-__lock__
	/tests/locks-45487402d7e545e6a88ef0756c2ccaa4
	/tests/locks-272ee302f8624d9b80ef62550a038073-__lock__
	/tests/locks-e116811a33124ddd8327114e7831c756
	/tests/locks-005f17afba1c4fdca30b209cc08c1d9f
	/zookeeper
	/zookeeper/quota