Singer-songwriter Joe Purdy walks the fine line between folk and country — as those genres continue to change meaning and significance — with evocative lyrics, and a melancholy voice. He shot into the public eye when his song “Wash Away” landed on ABC’s hit series “Lost,” although he had released two solid albums before that. Now, a veteran who has recorded more than a dozen records, Purdy has shown himself to be both a prolific and consistent solo musician.