Pull request: quick2wire upgrade + Mifare protocol

Hi Dany,

First of all, thanks for providing this library. It's extremely useful and it helped a lot in one of my Raspberry Pi projects. This pull request contains two things:

(1) It seems that the quick2wire library you included was an older one which didn't work with the current Raspbian distribution. I simply upgraded it. It's working fine now.

(2) I added a class, Mifare.py, which implements large parts of the Mifare protocol. You can now read from and write to Mifare cards with this library.

Let me know if you have any questions.

Cheers,
-Oliver