Construction of empirical distribution for list of epidist objects

[adamkucharski]

In discussion of converting epireview to epidist distribution objects, we discussed creating a list of epidist objects. As these could have different functional forms (e.g. gamma, lnorm), would be useful to have a function that takes a list of epidist objects as input, then converts to an empirical distribution by sampling draws randomly from different distributions (e.g. using ecdf), perhaps with option to weight by certain characteristic when sampling (e.g. by study size in epidist)

[joshwlambert]

The distribution aggregation added in #388 might have superseded this feature request. I will give it some more thought before closing.

If there is something outlined in this issue that cannot be achieved using aggregate() please let me know and we can work on incorporating it.