Added Av as output

This is a minor release that simply adds the attenuation (Av) as an output of the code. This is given for the disk and bulge components, separately, since they can have different attenuations. Note however that even then this is an "effective" Av, because the SEDs of bulges and disks are composite SEDs averaged over multiple Av values. The code was also updated to the latest library API, with no change to its behavior.