Refactor chesspp::exception, change to JSON instead of XML

I refactored the exception class heavily, it looks like a proper exception class now. I also changed config.xml to config.json - JSON will be better in the long run than XML.

Note: Please pull #21 first

The actual commit of interest: https://github.com/LB--/ChessPlusPlus/commit/af8cace60255320fc4b826e7219d36c1e1f11297