Per-chromosome heritability estimates

[dmgatti]

Enhancement: Gary suggested adding an option to est_herit() that would allow for heritability estimates on each chromosome. I've been doing it with 'regress' by putting all 20 per-chromosome kinship matrices into the model and getting the variance components for each chromosome. To be clear, these kinship matrices are obtained using calc_kinship() with type = "chr".

[kbroman]

I like the idea, but it seems like some hefty calculations just for this. I'd rely on the regress package, but sadly it's been "orphaned".