possible to reintroduce type hints for php and/or type hint in comments?
Hi,

thanks for such a nice library and all the work that goes into it. @GreyCat @markbook2 I remember that the type hints for the php runtime were removed due to problems with nullable types? How hard would it be to add them back now that php 7.1 and 7.2 are out with type hints like `?Foo` - maybe behind a command line switch for example `--add-php-type-hints` or by using two php runtime targets on the command line e.g `--target php` (no type hints) and `--target php:7.1+` (has type hints)?  

Also, how hard would it be to type hint arrays of objects by using doc comments? E.g

```php
...
/*
 * @return Foo[]
 */
public function foos(): array {
    ...
}
...
```
This would help IDEs to autocomplete for example in foreach etc. The second one is possible by including it in the `doc:` part of the .ksy file but a automatic solution would be nice.