add cursor support

gcloud/datastore/connection.py

@@ -226,7 +226,7 @@ def run_query(self, dataset_id, query_pb, namespace=None):
 
     request.query.CopyFrom(query_pb)
     response = self._rpc(dataset_id, 'runQuery', request, datastore_pb.RunQueryResponse)
-    return [e.entity for e in response.batch.entity_result]
+    return ([e.entity for e in response.batch.entity_result], response.batch.end_cursor, response.batch.more_results, response.batch.skipped_results)
 
   def lookup(self, dataset_id, key_pbs):
     """Lookup keys from a dataset in the Cloud Datastore.

gcloud/datastore/query.py

@@ -308,8 +308,19 @@ def fetch(self, limit=None):
     if limit:
       clone = self.limit(limit)
 
-    entity_pbs = self.dataset().connection().run_query(
+    entity_pbs, end_cursor, more_results, skipped_results = self.dataset().connection().run_query(
         query_pb=clone.to_protobuf(), dataset_id=self.dataset().id())
 
+    self._cursor = end_cursor
     return [Entity.from_protobuf(entity, dataset=self.dataset())
             for entity in entity_pbs]
+
+  def cursor(self):
+    return self._cursor
+
+  def with_cursor(self, start_cursor, end_cursor=None):
+    if start_cursor:
+      self._pb.start_cursor = start_cursor
+    if end_cursor:
+      self._pb.end_cursor = end_cursor
+