Implement "crc16" client option for redis-cluster.

By default Predis chooses automatically which hash generator to use:
if a suitable version of ext-phpiredis is loaded (that is, a version
that implements the phpiredis_utils_crc16() function) it uses the new
Predis\Cluster\Hash\PhpiredisCRC16 generator, otherwise it falls back
to the usual pure-PHP Predis\Cluster\Hash\CRC16 generator.

src/Configuration/Options.php

@@ -50,6 +50,7 @@ class Options implements OptionsInterface
             'commands' => 'Predis\Configuration\Option\Commands',
             'exceptions' => 'Predis\Configuration\Option\Exceptions',
             'prefix' => 'Predis\Configuration\Option\Prefix',
+            'crc16' => 'Predis\Configuration\Option\CRC16',
         );
     }