Imprinting: revise haplotypic values

[gregorgorjanc]

@david20011999 has hv() function at https://github.com/HighlanderLab/dlcarbonell_gametic_models/blob/a375b40207791c24c1f49b6ea0887d5e80d58500/functions.R#L163 where he is effectively/kind-of calculating gv()/2 but for targeted haplotype. We should look into that and see how to add bv()-like functionality so we capture both aspects.

Also, we should look how this bv()-like functionality resembles GCA-functionality in https://github.com/search?q=repo%3Agaynorr%2FAlphaSimR%20gca&type=code