/** Implementation of Raman, Raman and Rao's [1] proposal for rank/select capable
* data structures, it achieves space nH_0, O(sample_rate) time for rank and O(log len)
/** Implementation of Raman, Raman and Rao's [1] proposal for rank/select capable
* data structures, it achieves space nH_0, O(sample_rate) time for rank and O(log len)