Add list options

As the storage stores more objects, the size of the list of the objects also increase. Therefore the filter of list is needed. So, I added options of the list command.

usage:

	storage.list('mycontainer', { prefix: 'IMG_', limit: 20})
		.then(function(result) {
			console.log(JSON.parse(result));
		});

Available options are limit, marker, end_marker, prefix, format, delimiter and path. Details are in http://docs.openstack.org/api/openstack-object-storage/1.0/content/GET_showContainerDetails_v1__account___container__storage_container_services.html