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/Protocol/ProtocolInterface.php

@@ -0,0 +1,40 @@
+<?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\Protocol;
+
+use Predis\Command\CommandInterface;
+use Predis\Connection\ComposableConnectionInterface;
+
+/**
+ * Interface that defines a protocol processor that serializes Redis commands
+ * and parses replies returned by the server to PHP objects.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+interface ProtocolInterface extends ResponseReaderInterface
+{
+    /**
+     * Writes a Redis command on the specified connection.
+     *
+     * @param ComposableConnectionInterface $connection Connection to Redis.
+     * @param CommandInterface              $command    Redis command.
+     */
+    public function write(ComposableConnectionInterface $connection, CommandInterface $command);
+
+    /**
+     * Sets the options for the protocol processor.
+     *
+     * @param string $option Name of the option.
+     * @param mixed  $value  Value of the option.
+     */
+    public function setOption($option, $value);
+}