Editor's Note: As we head into the promise of a new year, The Union takes one last look back at the top 11 stories of 2011 and the impact they had on our community. The week-long series runs through Saturday, Dec. 31. Today we review our coverage of the homeless, which began with the death of William "Billy" Kelly, a homeless man who was found frozen to death in Nevada City on Feb. 27.Old Man Winter visited Nevada County with a vengeance in late February, dropping an estimated three feet of snow in some parts and pounding overnight temperatures into …