Zagg has announced the release of its new Bluetooth keyboard lineup for the iPad Pro and iPad mini 4. Three new iPad mini 4 keyboards include the Slim Book ($120), Folio with backlit keys ($100), and Folio with non-backlit keys ($80), which will be available for order on Sept. 15 for the Slim Book and Sept. 25 for the Folio models. Two new iPad Pro keyboards are also coming in November — the Messenger Universal ($70) and the Slim Book Pro ($140).…