added DiffUtils dependency

[navidaminnn]

I've added the dependency and made the appropriate changes in Manip.takeDiff to utilize the library. Given I'm on Windows and haven't been able to see how the .diff file is currently formatted, I wasn't entirely sure on how to output the diff.

I've attached a screenshot showing how the diff is shown using the library. If it's different from how the diffs look using the diff command, let me know and I'll change it to match it better.

[fhackett]

Note for me, so I don't forget: this is pending the removal of .toList from the proposed code, because difflib works better with O(1) indexing structures rather than linked lists, and the output of os.read.lines is an array already.