vignette: discussion of AIL; some edits to intro
vignette: small additions, including using args by name throughout
Refs for CC and MAGIC
Add date for Kover et al
vignette: missing period in a ref
Small change in description of ccgen arg to sim_do_pedigree

 - ccgen arg, if length 1, expanded to length npairs, by simply
   repeating
vignette: sim_do_pedigree; add ref to Broman (2012) re preCC