Added phpdoc_separation fixer

The idea here is to go from:

```php
    /**
     * @param EngineInterface $templating
     * @return void
     */
```

to 

```php
    /**
     * @param EngineInterface $templating
     *
     * @return void
     */
```
For me adding a single newline inside of docs with changing all newlines in that doc is a bug.
Then we could wait one more day and merge it without bug...