sstables: add convenience constructors for filter type
sstables: add convenience constructors for filter type

Signed-off-by: Glauber Costa <f8b79557d19b40666ebe336545a0b6178af65685@cloudius-systems.com>

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