Currently if a user wants SNP allele frequencies together with SNP effects, they have to call 2 methods and join/merge the resulting dataframes themselves.

It would be simpler IMO if we just added in the effects to the SNP allele frequencies.

E.g., we could change the signature of the Ag3.snp_allele_frequencies() to add an effects=True parameter. If True (default) then the effects would be automatically included in the resulting dataframe.