Hotfix/fqcn parameter type hints

This PR introduces FQCNs for type-hints in generated method signatures. This is a BC break, but it is necessary to use the code generator when the generated code is not placed on a dedicated file.

Before:

```php
public function doFoo(Foo $foo) {}
```

After

```php
public function doFoo(\Foo $foo) {}
```

This PR also takes into account the new PHP 5.4 `callable` data type when generating code.