Create and return a dataframe of ped.id, person1.id, person2.id, and ibd information from merlin
ibd.df.merlin(ibd.dat)data.frame with posterior IBD data from Merlin, with column names: FAMILY, ID1, ID2, MARKER
The returned data.frame, call it df, with the following elements:
df\$ped.id: pedigree id
df\$person1.id: df\$person2.id: identifiers for the relative pair within a pedigree
df\$post0: matrix objects that can be referenced from df. Each df\$post1: is a matrix with posterior ibd sharing probabilities for df\$post2: relative pairs (rows) at each chromosome position (columns)