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/ConnectionInterface.php

@@ -0,0 +1,63 @@
+<?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;
+
+use Predis\Command\CommandInterface;
+
+/**
+ * Defines a connection object used to communicate with one or multiple
+ * Redis servers.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+interface ConnectionInterface
+{
+    /**
+     * Opens the connection.
+     */
+    public function connect();
+
+    /**
+     * Closes the connection.
+     */
+    public function disconnect();
+
+    /**
+     * Returns if the connection is open.
+     *
+     * @return bool
+     */
+    public function isConnected();
+
+    /**
+     * Write a Redis command on the connection.
+     *
+     * @param CommandInterface $command Instance of a Redis command.
+     */
+    public function writeCommand(CommandInterface $command);
+
+    /**
+     * Reads the reply for a Redis command from the connection.
+     *
+     * @param  CommandInterface $command Instance of a Redis command.
+     * @return mixed
+     */
+    public function readResponse(CommandInterface $command);
+
+    /**
+     * Writes a Redis command to the connection and reads back the reply.
+     *
+     * @param  CommandInterface $command Instance of a Redis command.
+     * @return mixed
+     */
+    public function executeCommand(CommandInterface $command);
+}