Peter White Television EditorPopstar Alicia Keys is to exec produce a feature-length documentary about six iconic African American female entertainers for PBS.American Masters: How It Feels To Be Free will tell the story of Lena Horne, Abbey Lincoln, Nina Simone, Diahann Carroll, Cicely Tyson and Pam Grier and how they challenged an entertainment industry deeply complicit in perpetuating racist stereotypes, and transformed themselves and their audiences in the process.The doc, which will air in