Determine which models we are going to explore

[maxbiostat]

Contrary to what you might think, there are a plethora of models out there, with all sorts of likelihood functions and all. See #10.

All epidemic models that have an R0 that can be written as a Gamma ratio are interesting in principle. Notice that if, say, R0 = mu/(nu + gamma), that's interesting, because the sum of two Gamma r.v.s is Gamma, and hence this would qualify.