Converted en-passant to uint8
Store king square as uint8
Converted position.color to uint8
Updated tests for uint8 king square and color
Added test for 50 moves rule
Added 50 moves rule detection
Use black/white winning constants to define decisive advantage
Added 50 moves rule to game status
Added 50 moves rule in search
Added nodes per seconds and elapsed time helpers
Converted duration to int64