Added phpdoc_separation fixer

The idea here is to go from:

```php
    /**
     * @param EngineInterface $templating
     * @return void
     */
```

to 

```php
    /**
     * @param EngineInterface $templating
     *
     * @return void
     */
```
Yeh, but our existing fixers are affected by the same bug. That's my point.

That said, I'm not really bothered about waiting a day or two for this to go through. :)