Added a function _locate_line() that does a binary search for the chunk that contains the line to be searched and then follows up with another binary search within the chunk to get to the line itself. The function returns the chunk and the row which contains the line number.

Tested by running ReviewBot (cpplint, pep8 -- on 1 Cpp file and 1 python script) with the changes and the comments were updated against the correct line numbers in the file diff.