In the wake of the mass shooting in Aurora, Colo., Americans took to social media to express their views on guns and violence.     A reader sent us one Facebook post about the extent of gun violence in the United States. It said, "USA is #1 in gun violence. Nearly 100,000 people get shot every year. That's 270 people a day and 87 dead because of gun violence every day."     In this item, we’ll look at the first part of that claim -- that the "USA is #1 in gun violence." ...