major rewrite
- move to the bsdiff4 python extension module
- implement command line arguments
- make future-proof ;)
Huge-ass refactor.

(or a huge ass-refactor...)
Remove unused execute_bsdiff function.

Orochimarufan removed it before, but it must've magically reappeared when I merged his changes with my stashed
changes.
Return 0 when there is nothing to do.

Before it was returning 1, which is wrong because it's not an error when there is no work to be done.
Chmod, again.

Dammn you windows users.
Merge pull request #3 from GUIpsp/master

Make patchgen.py executable.