By Herbert Villarraga NEAR KREMINNA, Ukraine (Reuters) -Russian and Ukrainian forces exchanged artillery fire at the front line in Ukraine on Friday, even after Moscow said it had ordered its troops to stop shooting for a unilateral truce that was firmly rejected by Kyiv. President Vladimir Putin ordered the 36-hour ceasefire from midday on Friday to observe Russian Orthodox Christmas. Ukraine has said it has no intention to stop fighting, rejecting the purported truce as a stunt by Moscow to buy time to reinforce troops that have taken heavy losses this week. “What ceasefire? Can you hear?” s…