Major rewrite

Hi Miguel.
Thank you very much for having your code in the public domain and on GitHub. It is much appreciated! ;-)

Lately I have spent a lot of time recently refactoring your rfid ibrary. Here is a summary of my changes:
- Renamed library from RFID to MFRC522 (RFID seemed to generic).
- Register names changed to comply with datasheet.
- Global defines moved into class.
- All constants, functions and parameters are now commented in English.
- Code refactored, most function names have changed.
- Now supports ISO-14443-3 anti collission and 4/7/10 byte UIDs (cascade levels).
- Added functions for MIFARE Classic Decrement/Increment/Restore/Transfer and MIFARE Ultralight Write.
- New examples written.

From a functional point of view, the most important changes are that the library now knows about 7 and 10 byte UIDs (those were ignored before) and that it can perform the anti collision procedure specified in ISO-14443-3.

I learned a lot about ISO-14443-3 and MIFARE chips while working with the library.
A lot of that information is now collected at the top of MFRC522.h,

I would like to offer you all my changes back into your repository in the hope that it is welcomed, and believing that a common codebase will be beneficial to the community.
However if you find the changes too invasive (and I would understand that) I will proceed and offer my library as an alternative to yours.

Again, thank you for a great starting point. It sure helped my to get going.
I look forward to receive your response.

Best regards
  Søren.