Edgar Oliverhas a voice you’ll never forget: part Bela Lugosi, part Count Chocula. You may have heard him tell stories of growing up in Savannah in the 1960s, with a smothering, compulsive mother who shared her paranoid, terrified state with her children, Helen and Edgar. His tales of growing up are pulled together in “Helen and Edgar”, a kind of a spoken memoir being performed at Dartmouth’s Warner Bentley Theaterat 7:00pm tonight and Wednesday.