By Caleb Davis (Reuters) -Thirteen people were killed when a fire tore through a crowded nightclub in the Russian city of Kostroma in the early hours of Saturday, officials said. The blaze broke out at about 2:30 a.m. in Polygon – an entertainment venue with a bar, restaurant and large dance floor – after a man shot a flare gun at the ceiling, the TASS news agency said. “Very quickly the room began to fill with acrid smoke and the evacuation exits were difficult to see. There was pushing and panic,” the agency reported, citing an eyewitness in Kostroma, which lies some 300 km (190 miles) north…