Add support batch

Please add support batch for multi insert / update / delete / select.

For example:
`$tnt = Tarantool('localhost', 3301);
$tnt->connect();
$batch = $tnt->batch();
$batch->insert();
$batch->update();
$batch->delete();
$batch->select();
$result = $batch->exec();`

Result like:
`array {
'key' => array(result),
'key' => array(result)
}`
