Expand getPed() with a recursive argument

[gregorgorjanc]

Describe the solution you'd like We would like to call getPed() and get deep pedigree

Additional context Currently we get 1 generation, so maybe that could stay as default, but modifying the number of generations by an argument would recursively parse the SP$pedigree object (throw an error if we are not tracking the pedigree)

[gregorgorjanc]

We discussed with @gaynorr that we could add an argument to pull additional generations of pedigree from SP$pedigree, which I will do when we will need this functionality (or someone beats me to it).

There is a challenge that the above approach might not work with selfed populations in the way we want - parents will be off for some number of generations. We can add additional argument to handle such cases, but first we should do the simpler functionality first.