[ajqezkui] Minard chess viewer

Inspired by Charles Minard's map of Napoleon's Russian campaign (also popularized by Edward Tufte), create an artistic chess game replay viewer in the same style.

At any stage of the game, selecting a piece (or, by default, the most recent piece) draws its "tail", which gives the past trajectory of the piece.  The tail starts out broad and most translucent at the piece's the starting position, and becomes thinner and less translucent for each move.  The translucency is to help prevent confusion in overlap.  A piece might leave and return to a square, so the levels of translucency and thinner tail make clear which movements happened later.

Also depict in the same matter, but different color, every opponent piece that this piece captured.  The tail thins to nothing at the point of capture.

Also depict (this might be getting too noisy) in the same matter every opponent piece this piece attacks, and every opponent piece that attacks this piece.  Beams denote attacks.  Maybe limit it to "credible" attacks that wouldn't result in disadvantage if capturing on a null move.