Kiwix/ZIM incremental updates/17-23 June report

As part of the first week of GSoC 13, I completed a zimdiff tool, which can be used to generate the diff_file between two ZIM files. The zimdiff tool takes two ZIM files as input, computes the difference between them and writes it into a separate file(diff_file). The logic is as follows: start_file+diff_file=end_file.

The code is available here: https://github.com/kiranmathewkoshy/zimdiff