Washington (AFP) – The National Rifle Association is the central and fiercest promoter of gun rights in America, and is again holding its annual convention days after a mass school shooting. Just like the NRA’s meeting after the 1999 Columbine attack, which defined an era of gun massacres in America’s schools, the gathering opening Friday in Houston follows the killing of 19 children and two teachers in a Texas classroom. The NRA has been weakened by scandal and turmoil, but remains the main force dedicated to advocating for the owners of the tens of millions of weapons that are readily obtain…