added simple burrows-wheeler transform function. not memory conservative.
added function for inversing burrows-wheeler transform sequence to reconstruct original sequence.
added function to retrieve pattern match occurrence frequencies by using burrows-wheeler.
a faster and more memory efficient version of burrows-wheeler pattern match occurrence frequency function added.
added function for partial suffix array construction.
changed data structure for partial suffix array from list of tuples to dictionary, for later convenience.
edited burrows-wheeler exact matching to return the location of matched patterns. used partial suffix array for location tracking.