NAME
    Algorithm::Metric::Chessboard - Calculate distances on a square grid
    with optional wormholes (the 'chessboard metric').

DESCRIPTION
    Calculates minimum number of moves between two points in a game played
    on a square grid, where one move is a jump from a point to a horizontal,
    vertical or diagonal neighbour.

    With no other features, the number of moves taken to go from the point
    "(x1, y1)" to "(x2, y2)" *would* be quite simple:

      d( (x1, y1), (x2, y2) ) = max( abs( x1 - x2 ), abs( y1 - y2) )

    However within the space are "wormholes" which allow you to travel
    between any two distant points in one move, so the actual number of
    moves may be smaller than the above. Wormhole travel costs a fixed
    number of moves.
