A federal appeals court has given a convicted murderer the go-ahead to pursue a lawsuit against the prison officials who blocked him from seeing his victim’s death certificate.The 7th U.S. Circuit Court of Appeals on Tuesday did not rule on the merits of Kevin A. Williams’ allegation that officials at Pontiac Correctional Center in central Illinois violated his First Amendment rights when they confiscated the certificate after it arrived in the mail.But the court revived the claims Williams leveled against the …