Checks for INI, JSON, XML and YAML file validation

I needed some checks validating different files in another project. Maybe the community can benefit from it, so i pull-requested them:

* [Check\IniFile](https://github.com/frne/ZendDiagnostics/blob/file_validation_test/src/ZendDiagnostics/Check/IniFile.php)
* [Check\JsonFile](https://github.com/frne/ZendDiagnostics/blob/file_validation_test/src/ZendDiagnostics/Check/JsonFile.php)
* [Check\XmlFile](https://github.com/frne/ZendDiagnostics/blob/file_validation_test/src/ZendDiagnostics/Check/XmlFile.php)
* [Check\YamlFile](https://github.com/frne/ZendDiagnostics/blob/file_validation_test/src/ZendDiagnostics/Check/YamlFile.php)

Feedback welcome ;)