ASTERIXDB-1778: Optimize the edit-distance-check function - Only calculate 2 * (threshold + 1) cells, rather than all cells per row. - Terminate the calculation steps early when it become obvious that the possible edit-distance value is greater than the given threshold. There is no reason to compute all cells in the 2 dimensional array. - Move the location of IListIterator to Hyracks since we now have a CharacterIterator in a String. Change the name to ISequenceIterator. - Add the section for the function in the manual. - Remove letter counting filtering method since it is only applicable for the string in ASCII range (0 ~ 127).