introduce compatible support for JsonSerializable

For PHP 5.3.x environment, 
this is enhancement for Json Component for JsonSerializable compatiblity.

@see http://php.net/jsonserializable.jsonserialize.php

NOTES : now implementation needs before using
```
class_alias('Zend\Json\JsonSerializable', 'JsonSerializable');
```
so, if this proposal is acceptable, needs to write it documentation.