Release v1.6.0 (#324)

* Update version and changelog for v1.6.0
* Update docs
diff --git a/docs/epy/toc-googleapiclient._auth-module.html b/docs/epy/toc-googleapiclient._auth-module.html
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+++ b/docs/epy/toc-googleapiclient._auth-module.html
@@ -0,0 +1,46 @@
+<?xml version="1.0" encoding="ascii"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+          "DTD/xhtml1-transitional.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+<head>
+  <title>_auth</title>
+  <link rel="stylesheet" href="epydoc.css" type="text/css" />
+  <script type="text/javascript" src="epydoc.js"></script>
+</head>
+
+<body bgcolor="white" text="black" link="blue" vlink="#204080"
+      alink="#204080">
+<h1 class="toc">Module _auth</h1>
+<hr />
+  <h2 class="toc">Functions</h2>
+  <div class="private">
+    <a target="mainFrame" href="googleapiclient._auth-module.html#authorized_http"
+     >authorized_http</a><br />  </div>
+  <div class="private">
+    <a target="mainFrame" href="googleapiclient._auth-module.html#default_credentials"
+     >default_credentials</a><br />  </div>
+  <div class="private">
+    <a target="mainFrame" href="googleapiclient._auth-module.html#with_scopes"
+     >with_scopes</a><br />  </div>
+  <h2 class="toc">Variables</h2>
+  <div class="private">
+    <a target="mainFrame" href="googleapiclient._auth-module.html#HAS_GOOGLE_AUTH"
+     >HAS_GOOGLE_AUTH</a><br />  </div>
+  <div class="private">
+    <a target="mainFrame" href="googleapiclient._auth-module.html#HAS_OAUTH2CLIENT"
+     >HAS_OAUTH2CLIENT</a><br />  </div>
+<hr />
+<span class="options">[<a href="javascript:void(0);" class="privatelink"
+    onclick="toggle_private();">hide&nbsp;private</a>]</span>
+
+<script type="text/javascript">
+  <!--
+  // Private objects are initially displayed (because if
+  // javascript is turned off then we want them to be
+  // visible); but by default, we want to hide them.  So hide
+  // them unless we have a cookie that says to show them.
+  checkCookie();
+  // -->
+</script>
+</body>
+</html>