Allow two different generators to correlate data

As a user I want to create a list of pojos, and I also want to have another list of different pojos which have fields that reference the IDs of the first list. This way I don't have to manually set the referencing fields after the fact of pojo generation.

Start by reading the library's POJO generation API and how generated objects receive randomized field values. Determine how two generator runs could share identifiers and how referenced fields would be selected, then define an API and tests that demonstrate correlated lists and verify the resulting references.

Written by the indexing model from the issue text.