Release v1.6.0 (#324)

* Update version and changelog for v1.6.0
* Update docs
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+<h1><a href="dataflow_v1b3.html">Google Dataflow API</a> . <a href="dataflow_v1b3.projects.html">projects</a> . <a href="dataflow_v1b3.projects.locations.html">locations</a> . <a href="dataflow_v1b3.projects.locations.jobs.html">jobs</a> . <a href="dataflow_v1b3.projects.locations.jobs.messages.html">messages</a></h1>
+<h2>Instance Methods</h2>
+<p class="toc_element">
+  <code><a href="#list">list(projectId, location, jobId, startTime=None, pageSize=None, x__xgafv=None, pageToken=None, minimumImportance=None, endTime=None)</a></code></p>
+<p class="firstline">Request the job status.</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(projectId, location, jobId, startTime=None, pageSize=None, x__xgafv=None, pageToken=None, minimumImportance=None, endTime=None)</code>
+  <pre>Request the job status.
+
+Args:
+  projectId: string, A project id. (required)
+  location: string, The location which contains the job specified by job_id. (required)
+  jobId: string, The job to get messages about. (required)
+  startTime: string, If specified, return only messages with timestamps >= start_time. The default is the job creation time (i.e. beginning of messages).
+  pageSize: integer, If specified, determines the maximum number of messages to return. If unspecified, the service may choose an appropriate default, or may return an arbitrarily large number of results.
+  x__xgafv: string, V1 error format.
+  pageToken: string, If supplied, this should be the value of next_page_token returned by an earlier call. This will cause the next page of results to be returned.
+  minimumImportance: string, Filter to only get messages with importance >= level
+  endTime: string, Return only messages with timestamps < end_time. The default is now (i.e. return up to the latest messages available).
+
+Returns:
+  An object of the form:
+
+    { # Response to a request to list job messages.
+    "nextPageToken": "A String", # The token to obtain the next page of results if there are more.
+    "jobMessages": [ # Messages in ascending timestamp order.
+      { # A particular message pertaining to a Dataflow job.
+        "messageImportance": "A String", # Importance level of the message.
+        "messageText": "A String", # The text of the message.
+        "id": "A String", # Identifies the message. This is automatically generated by the service; the caller should treat it as an opaque string.
+        "time": "A String", # The timestamp of the message.
+      },
+    ],
+  }</pre>
+</div>
+
+<div class="method">
+    <code class="details" id="list_next">list_next(previous_request, previous_response)</code>
+  <pre>Retrieves the next page of results.
+
+Args:
+  previous_request: The request for the previous page. (required)
+  previous_response: The response from the request for the previous page. (required)
+
+Returns:
+  A request object that you can call 'execute()' on to request the next
+  page. Returns None if there are no more items in the collection.
+    </pre>
+</div>
+
+</body></html>
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