chessmatch check

Hi Philip, you can document the init instead of the class and I won't dock you for it but as a matter of readability it's nice when the class has its own doc block even if its similar to its parent. The reason is that changes to attributes can happen in child classes and it's nice to be explicit about exactly what will be found in the class instead of leaving whoever is reading it to wonder whether or not you forgot to add a docstring or if the docstring is the same as its parent.