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.

Predis/Connection/ReplicationConnectionInterface.php

@@ -0,0 +1,48 @@
+<?php
+
+/*
+ * This file is part of the Predis package.
+ *
+ * (c) Daniele Alessandri <suppakilla@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Predis\Connection;
+
+/**
+ * Defines a group of Redis servers in a master/slave replication configuration.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+interface ReplicationConnectionInterface extends AggregatedConnectionInterface
+{
+    /**
+     * Switches the internal connection object being used.
+     *
+     * @param string $connection Alias of a connection
+     */
+    public function switchTo($connection);
+
+    /**
+     * Retrieves the connection object currently being used.
+     *
+     * @return SingleConnectionInterface
+     */
+    public function getCurrent();
+
+    /**
+     * Retrieves the connection object to the master Redis server.
+     *
+     * @return SingleConnectionInterface
+     */
+    public function getMaster();
+
+    /**
+     * Retrieves a list of connection objects to slaves Redis servers.
+     *
+     * @return SingleConnectionInterface
+     */
+    public function getSlaves();
+}