SYDNEY , Australia (AFP) — Australia marked 20 years since its last mass shooting Thursday as campaigners warned its gun laws, which were severely tightened after the massacre, are being eroded. Thirty-five people died at the historic Tasmanian colonial convict site of Port Arthur in 1996 as lone gunman Martin Bryant, armed with semi-automatic weapons, went on the rampage. Now aged 48, he remains in jail after being sentenced to 35 life sentences without parole. […]