Added simple field of vision (circle).
Added simple field of vision, using line of sight.
Added versioning to savefile. Fixed bug with eating first letter of names read.
Added cell characteristics: seen, visible. Added invalidate_fov() for recalculation after each move or change. Added saving/loading cell.seen. Changed savefile version to 2.
Added tranparency to cells.
Added transparency saving. Changed savefile version to 3.
Tested glass wall effect: impassable but transparent.