Retwis ported to modern Redis data types.

The example (and related documentation at redis.io) was not updated for
5 years. Redis had no sorted sets and hashes when the original code was
written (!). An update was really needed.

We also use a modern PHP client now: Predis. A copy is shipped within
this repository to make life easier to newcomers trying Redis for the
first time via this example.

logout.php

@@ -0,0 +1,19 @@
+<?
+include("retwis.php");
+
+if (!isLoggedIn()) {
+    header("Location: index.php");
+    exit;
+}
+
+$r = redisLink();
+$newauthsecret = getrand();
+$userid = $User['id'];
+$oldauthsecret = $r->hget("user:$userid","auth");
+
+$r->hset("user:$userid","auth",$newauthsecret);
+$r->hset("auths",$newauthsecret,$userid);
+$r->hdel("auths",$oldauthsecret);
+
+header("Location: index.php");
+?>