A homeless maniac bludgeoned four other vagrants to death as they slept on the sidewalks of Chinatown early Saturday — bashing in their skulls one by one with a scavenged metal bar during a senseless predawn murder spree. Rodriguez “Randy” Santos is just 24, but already had what cops call a history of violent, random attacks when he allegedly approached his first victims, two men sprawled asleep side by side at Bowery and Doyers Street just before 2 a.m.