interface, autoloader

https://github.com/getjump/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md#3-%D0%9E%D0%B1%D1%8A%D1%8F%D0%B2%D0%BB%D0%B5%D0%BD%D0%B8%D0%B5-%D0%BF%D1%80%D0%BE%D1%81%D1%82%D1%80%D0%B0%D0%BD%D1%81%D1%82%D0%B2-%D0%B8%D0%BC%D0%B5%D0%BD-%D0%B8-use