Add R func probs_to_grid: reduce QTL probs to grid of pseudomarkers
probs_to_grid: check that grid not all true; check lengths
calc_genoprob: include crosstype, is_x_chr, sex, and cross_info as attributes
est_map: include is_x_chr as attribute
calc_genoprob: wasn't setting rownames properly
Add function calc_genetic_sim()

 - Calculate genetic similarity for all pairs of individuals, using
   genotype probabilities calculated from calc_genoprob.

 - Currently, returns proportion of matching genotypes; really should do
   proportion of matching haplotypes (turn genotype probabilities into
   probability of random allele).
Add function genoprob_to_alleleprob

 - converts probabilities from calc_genoprob from genotype probabilities
   to the allele probabilities (for a randomly chosen haplotype)
calc_genetic_sim: use allele probabilities rather than genotype probs