Added support for NamingStrategies.

This allows you to map entity propertynames to keys. Doctrine already supports this, but this module didn't.

For example:
```php
class User {
     protected $id;
     protected $userConnections;
}
```
mapping it to:

```json
{
  "id": 12,
  "connections": []
}
```

NamingStrategy class:
```php
namespace Application\Strategies;
use Zend\Stdlib\Hydrator\NamingStrategy\MapNamingStrategy;

class UserNamingStrategy extends MapNamingStrategy {
    protected $mapping = [
        'connections' => 'userConnections',
    ];

    public function __construct() {
        parent::__construct($this->mapping);
    }
}
```

config file:
```php
return array(
    'doctrine-hydrator' => array(
        'user' => array(
            'entity_class' => 'doctrine.entity',
            'object_manager' => 'doctrine.entitymanager.orm_default',
            'by_value' => true,
            'naming_strategy' => 'Application\Strategies\UserNamingStrategy',
            'strategies' => array(
                'userConnections' => 'Application\Strategies\EmbeddedCollectionStrategy',
            )
        ),
```