Discussion item: possibly useful functionality elsewhere

Not really an issue - should we start a discussion board?

Just to mention that some related (probably simpler) functionality to what I think is being implemented here is available at https://github.com/sbfnk/epimixr/blob/master/R/epidemic_age_dist.r - haven't looked yet in detail how the different methods are related but either way there might be useful code/inspiration there.

There are related functions there for estimating reproduction numbers and projecting immunity from seroprevalence/vaccination data. These could one day be brought under the same hat and/or linked up.