Add combine() template
Add combine() template

Similar to std::merge(), merges two sorted sequences. Duplicates, however,
are merged using a binary function parameter rather than duplicated.

scylladb/scylla,eklitzke/scylla,aruanruan/scylla,kjniemi/scylla,asias/scylla,rentongzhang/scylla,guiquanz/scylla,victorbriz/scylla,duarten/scylla,capturePointer/scylla,duarten/scylla,acbellini/scylla,bowlofstew/scylla,scylladb/scylla,scylladb/scylla,capturePointer/scylla,gwicke/scylla,rluta/scylla,stamhe/scylla,glommer/scylla,dwdm/scylla,bowlofstew/scylla,senseb/scylla,respu/scylla,rentongzhang/scylla,gwicke/scylla,avikivity/scylla,raphaelsc/scylla,shaunstanislaus/scylla,aruanruan/scylla,victorbriz/scylla,justintung/scylla,shaunstanislaus/scylla,kangkot/scylla,tempbottle/scylla,rluta/scylla,victorbriz/scylla,respu/scylla,justintung/scylla,stamhe/scylla,linearregression/scylla,gwicke/scylla,rentongzhang/scylla,wildinto/scylla,kjniemi/scylla,stamhe/scylla,duarten/scylla,asias/scylla,phonkee/scylla,respu/scylla,kangkot/scylla,avikivity/scylla,eklitzke/scylla,phonkee/scylla,kjniemi/scylla,raphaelsc/scylla,senseb/scylla,raphaelsc/scylla,scylladb/scylla,tempbottle/scylla,kangkot/scylla,tempbottle/scylla,eklitzke/scylla,asias/scylla,bowlofstew/scylla,acbellini/scylla,senseb/scylla,glommer/scylla,dwdm/scylla,rluta/scylla,aruanruan/scylla,shaunstanislaus/scylla,avikivity/scylla,acbellini/scylla,linearregression/scylla,justintung/scylla,linearregression/scylla,glommer/scylla,phonkee/scylla,guiquanz/scylla,guiquanz/scylla,wildinto/scylla,wildinto/scylla,capturePointer/scylla,dwdm/scylla