Support for FEN notation

[djnnvx]

FEN notation is a well known way to define a chess position in a simple string. It would be great if we could get a FEN string generated from the current position, because it makes it easier for testing it against other AIs.

To get more information against FEN string, you can check out this wiki which is really well made:
https://www.chessprogramming.org/Forsyth-Edwards_Notation

I can do it by myself but I just need to know if a value checks for each side whether we can castle or not.