made fin block size adjustable by default and added rand generator for fin
made fin block size adjustable by default and added rand generator for fin

RodolpheFouquet/gpac,RodolpheFouquet/gpac,rbouqueau/gpac,RodolpheFouquet/gpac,gpac/gpac,rbouqueau/gpac,gpac/gpac,gpac/gpac,gpac/gpac,rbouqueau/gpac,RodolpheFouquet/gpac,rbouqueau/gpac,rbouqueau/gpac,rbouqueau/gpac,gpac/gpac,gpac/gpac,RodolpheFouquet/gpac,rbouqueau/gpac,rbouqueau/gpac,gpac/gpac,RodolpheFouquet/gpac,gpac/gpac