In 1970, when I was still in high school, one of the albums I came across – shortly after writing a record-review column for my school paper – was the debut album by a man named Gil Scott-Heron. I snatched up the record because of the intriguing title of one track: “The Revolution Will Not Be Televised.” (Even then, anything involving TV beckoned me.) It knocked me out: spoken-word poetry, with musical accompaniment, that was somewhere between what once was called beat poetry and what someday would be called rap. It was honest, it was angry, and it was unlike anything I’d ever heard at the time. Tonight, the Unsung series salutes Gil-Scott Heron – who, over the decades, has been anything but unsung as a significant and original non-mainstream artist.