Americana that’s more than twang. Classic camp. A blues legend. Retro-pop. Those are four of the highlights on the Asheville music calendar these coming 30 days. Artist: Jimbo Mathus Venue: The Grey Eagle (patio) Date: Friday, Oct. 8, 6 p.m. Door: $15 If you only know Jimbo Mathus from his role as leader of Squirrel