FovType must be configurable by the user

[fabio-t]

Right now, Fov algorithms consider only a circle around the starting point, while Los algorithms consider a square. AStar considers a square, too.

Instead of trying to make this completely consistent, or to add yet more arguments to the contract, we should simply make this behaviour configurable.

• SQUARE fov implies manhattan distance

• CIRCLE fov implies "pseudo euclidean" distance (eg, floored and converted to int)