a class based implementation of dictdiffer

Hey I wrote a class based implementation of your dictdiffer module.

just instantiate it and you have the same methods as your module based functions diff, patch, ...

I think this has the advantage that one can easily make custom diffs for example str or other types, and it is even faster, see benchmarking.py

And I also found some bug in your implementation, if the dict changes from example {'a':{'a':1}} to {'a':1} your diff method fails, I added a new assertation in the testcase for that.

If you like my implementation, which takes most of the logic from your module I would be happy if you merge it.