Akari astrodust

[RaelynSullivan]

Added astrodust extension to the mbbtab type - mbbtab now has a mbb on the low frequency end, a splined tabulated regime in the middle and the linear astrodust model on the high frequency end (with smooth transitions between each regime). A new parameter nu_join, tells where the MBB should transition to the spline. The astrodust has a new SED sampling parameter called adScale (astrodust scale) which scales the astrodust up and down, and a new read statement to read in the astrodust file. The nu_join must be less than the lowest nu in the tabulated SED, and the highest value in the tabulated SED must not overlap with the lowest value in the astrodust table.
When sampling SED parameters and tabulated parameter in the MCMC you must do these two separately.