interface, autoloader

https://github.com/getjump/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md#5-%D0%A3%D0%BF%D1%80%D0%B0%D0%B2%D0%BB%D1%8F%D1%8E%D1%89%D0%B8%D0%B5-%D0%A1%D1%82%D1%80%D1%83%D0%BA%D1%82%D1%83%D1%80%D1%8B