Discovery of (7 R )-14-Cyclohexyl-7-{[2-(dimethylamino)ethyl](methyl) amino}-7,8-dihydro-6 H -indolo[1,2- e ][1,5]benzoxazocine-11-carboxylic Acid (MK-3281), a Potent and Orally Bioavailable Finger-Loop Inhibitor of the Hepatitis C Virus NS5B Polymerase