`oneMarkerDistribution()` should accept ped lists

[magnusdv]

library(pedprobr, quietly = T)
peds = setMarkers(list(singleton(1), singleton(2)), 
                  locusAttributes = list(alleles = 1:2))

oneMarkerDistribution(peds, ids = 1:2, partialmarker = 1)
#> Error: Input is not a `ped` object

^{Created on 2020-01-24 by the reprex package (v0.3.0)}