Supernova Additions

[joezuntz]

Need to

• Add the Pantheon Plus likelihood https://github.com/PantheonPlusSH0ES/DataRelease/blob/main/Pantheon%2B_Data/5_COSMOLOGY/cosmosis_likelihoods/Pantheon%2B_only_cosmosis_likelihood.py changing the (1+zcmb) * D_A -> D_C

• Implement Equations A9 - A12 of https://www.aanda.org/articles/aa/pdf/2001/46/aah2780.pdf to optionally analytically marginalize over M

• Possibly add Tamara's faster integral to generate distances.