removed the homozygous type from the totalLogLikelihood, but treat it together with input_dat.higher as one data block. Reason is that model is bad at predicting hom-frequency, but good at low-freq variants. So we should let the model only compute those low-freq variants and lump all other sites into the rest.
changed all size_t to int after nasty bug caused by unsigned arithmetic mistake. made exponential approximate for small arguments