chess demo 2022

This is an attempt at chess. There is no stalemate detection. There is a corner case of moving into check by en passant capture, but otherwise it should do legal games.

Squares are highlighted:

• Blue means has legal moves (click to move it).
• Red means the square is attacked or defended by the inactive player.
• Green means the piece is pinned to the active king.

This is probably 4 days of work.