Vignettes showing how to simulate various crosses

[kbroman]

Add a series of vignettes showing how to simulate various cross types and create the files needed for R/qtl2, or to convert directly to an R/qtl2 cross2 object. Particularly useful for testing (e.g. of Issues rqtl/qtl2#140 and rqtl/qtl2#141 concerning DOF1 data, for which I have no examples).

• Diversity Outbred (DO) mice
• DOF1 (DO crossed to some common 9th strain)
• Collaborative Cross (CC, 8-way RIL by sibling mating)
• 8-way MAGIC lines
• 19-way MAGIC lines
• Heterogeneous stock (HS)
• 3-way AIL