large_bitmap: support for loading and saving the bitmap to raw ints
large_bitmap: support for loading and saving the bitmap to raw ints

Single-bit accessors are very slow, especially because we don't support
setting a bit to a value (just set to 1 and clear to 0).  This causes
loading and retrieving the contents of a bitmap to be painfully slow.

Fix by providing iterator-based load() and save() methods.  The methods
support partial load/save so that access to very large bitmaps can be
split over multiple tasks.

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