Removed nbits == 0 check
Added a modification that makes nbits at least 1
Added parameter checking to create_wavelet_tree()
Wrote a test that checks behaviour when using faulty params
Added a rank-query for the wavelet tree
Added a variable that stores number of filler bits
Minor bugfix in binary_search()
Bugfixing in wavelet_rank_query()
Minor bugfix in binary search
Minor bugfixes in rank algorithm
Added some tests for the rank-query