Make the jardiff.py fully cross-platform

Make the jardiff.py fully cross-platform. Thanks a lot for help me, the script is working on Windows as well as on UNIX platforms :smile:.

I do not know how to program in Python, i'm a .Net guy, some things can get better :smile: in code

In Windows requires Cygwin. After I send another pull request with information about its installation and required package.

Thanks a lot.
Hi Jake :smile:, unfortunately yes, ```javap``` on Windows doesn't play well with absolute paths. Unlike what happens on Linux (I've used Ubuntu 14.04), where you can use the absolute path for find the *.class files, on Windows (I've tested with Windows 8.1) it will cause "ERROR: File not found". 
The solution that remains cross-platform was set the base path of the *.class files as -classpath argument and pass the relative path of the *.class files without its extension for ```javap```.