Refactor C_Board class to struct + methods using reference

[mx-e]

• C Board state should be held in a struct
• All functions operating on C Board should use only a reference as parameter
• Ideally any memory needed by any function currently implemented as part of C_Board should be allocated together with the C_Board struct (legal moves, board scan, etc...)
• Ideally the refactored implementation should be faster or as fast as the current implementation