Release v1.6.0 (#324)

* Update version and changelog for v1.6.0
* Update docs
diff --git a/docs/dyn/pubsub_v1.projects.topics.subscriptions.html b/docs/dyn/pubsub_v1.projects.topics.subscriptions.html
index 02b2b2f..c89540c 100644
--- a/docs/dyn/pubsub_v1.projects.topics.subscriptions.html
+++ b/docs/dyn/pubsub_v1.projects.topics.subscriptions.html
@@ -75,27 +75,35 @@
 <h1><a href="pubsub_v1.html">Google Cloud Pub/Sub API</a> . <a href="pubsub_v1.projects.html">projects</a> . <a href="pubsub_v1.projects.topics.html">topics</a> . <a href="pubsub_v1.projects.topics.subscriptions.html">subscriptions</a></h1>
 <h2>Instance Methods</h2>
 <p class="toc_element">
-  <code><a href="#list">list(topic, pageSize=None, pageToken=None, x__xgafv=None)</a></code></p>
+  <code><a href="#list">list(topic=None, pageSize=None, pageToken=None, x__xgafv=None)</a></code></p>
 <p class="firstline">Lists the name of the subscriptions for this topic.</p>
 <p class="toc_element">
   <code><a href="#list_next">list_next(previous_request, previous_response)</a></code></p>
 <p class="firstline">Retrieves the next page of results.</p>
 <h3>Method Details</h3>
 <div class="method">
-    <code class="details" id="list">list(topic, pageSize=None, pageToken=None, x__xgafv=None)</code>
+    <code class="details" id="list">list(topic=None, pageSize=None, pageToken=None, x__xgafv=None)</code>
   <pre>Lists the name of the subscriptions for this topic.
 
 Args:
-  topic: string, The name of the topic that subscriptions are attached to. (required)
+  topic: string, The name of the topic that subscriptions are attached to.
+Format is `projects/{project}/topics/{topic}`. (required)
   pageSize: integer, Maximum number of subscription names to return.
-  pageToken: string, The value returned by the last `ListTopicSubscriptionsResponse`; indicates that this is a continuation of a prior `ListTopicSubscriptions` call, and that the system should return the next page of data.
+  pageToken: string, The value returned by the last `ListTopicSubscriptionsResponse`; indicates
+that this is a continuation of a prior `ListTopicSubscriptions` call, and
+that the system should return the next page of data.
   x__xgafv: string, V1 error format.
+    Allowed values
+      1 - v1 error format
+      2 - v2 error format
 
 Returns:
   An object of the form:
 
     { # Response for the `ListTopicSubscriptions` method.
-    "nextPageToken": "A String", # If not empty, indicates that there may be more subscriptions that match the request; this value should be passed in a new `ListTopicSubscriptionsRequest` to get more subscriptions.
+    "nextPageToken": "A String", # If not empty, indicates that there may be more subscriptions that match
+        # the request; this value should be passed in a new
+        # `ListTopicSubscriptionsRequest` to get more subscriptions.
     "subscriptions": [ # The names of the subscriptions that match the request.
       "A String",
     ],