sf-relate integration

[dinvlad]

This PR attempts to integrate SF-GWAS with SF-Relate by saving an encrypted relatedness mask file, which is later used by SF-Relate.

@froelich Could you please provide feedback if this is the right approach and place to do it?

Sister PR: hcholab/sfgwas#10

[froelich]

@dinvlad I think it is the right place to do it. I think that it can be slightly optimized by changing the return of signTestComposed . If we are in this workflow, signTestComposed should return the vector without calling PostprcoessSignTest. The vector will then contain -1s and 1s.

Then the lines 184 and 185 would become:

oblockInv = crypto.CAddConst(cps, oblockInv, -1.0)
oblockInv := crypto.CMultConstRescale(cps, oblock, -0.5, false)

This is a minor optimization, removing PostprcoessSignTest in this case saves one level and a few operations (add, mult and rescale).