Our occasional series “Secret History” features profiles of classic D.C. albums as a way of looking back at the District’s contributions to music over time. This go ’round, we pay tribute to the Delta 72’s mighty burner The R&B of Membership (Touch and Go, 1996). The Delta 72 burst out of D.C. in the early ’90s peddling a fiery mix of brash Capitol City hardcore and gritty southern soul, relentlessly distorted guitar rumble and…