Table of "known cases"

[HenrikBengtsson]

I've added vignette https://marshal.futureverse.org/articles/known_cases.html that currently only holds a table. The data from that table is pulled from https://github.com/HenrikBengtsson/marshal/blob/develop/inst/known_cases.json.

This is a first attempt at providing an overview of what happens when "exporting" different types of objects in R. I anticipate that this table will keep growing as we get aware of more cases.