[phpdoc] Add API documentation.

This is a starting point to add a documentation of the whole set of APIs and
classes of Predis. The next step will be to actually improve and extend it.

lib/Predis/Protocol/IProtocolProcessor.php

@@ -14,8 +14,27 @@ namespace Predis\Protocol;
 use Predis\Commands\ICommand;
 use Predis\Network\IConnectionComposable;
 
+/**
+ * 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 IProtocolProcessor extends IResponseReader
 {
+    /**
+     * Writes a Redis command on the specified connection.
+     *
+     * @param IConnectionComposable $connection Connection to Redis.
+     * @param ICommand $command Redis command.
+     */
     public function write(IConnectionComposable $connection, ICommand $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);
 }