Pedigree based inbreeding estimation

[timothymillar]

Related to #845. Estimation of inbreeding coefficients from pedigree data does not require computation of the full kinship matrix. Hamilton and Kerr (2017) outline an approach to this which works for both diploid and autopolyploid pedigrees. The efficiency of this method is dependent on pedigree complexity, but it should generally be much faster than computation of the full kinship matrix.