Updated calc_dist() and optimize_tour()

1. Updated calc_dist formula to this:		
     return round(math.sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2)),0)

2. Replaced optimize_tour() with a better and more concise version.  It now doesn't go through unnecessary iterations - it will stop once two consecutive cycles reach the same result.  It also report the cycle# and occasional tour stop status during runtime.  Not sure if we eventually want to keep that, but I'd like to leave it in for now.