Update Configuration API

Fixes #13 

```php
return [
    'htimg' => [
        'filters' => [
            'my_filter' => [
                'type' => 'filter_type',
                'options' => [
                    // .....
                    'image_loader' => 'simple',
                    'loader_options' => [
                        'root_path' => 'data/images/uploads', // this is the new part
                    ]
                ]
            ]        
        ]
    ]
];
```