Alex Luna, who was born with a shortened right arm that stops at the elbow, stands out among the other players on the Belleville Knights of Columbus Little League team. But to describe the 12-year-old honor student as handicapped would be misleading. The kid can play.  “He’s getting better every year,” said Bob Abramson, Alex’s coach for the last three years. “It is amazing. Simply amazing.” Indeed, after meeting Alex Luna, you almost have no choice but to expand your idea of what’s possible. Alex, who this year is an outfielder and relief pitcher for the Knights of Columbus team, also takes …