[ ] Enforce valid parameters.
    Some functions will cause a crash when called with invalid parameters (e.g.
    mifare_classic_authenticate() with a NULL key).
[ ] MAD and MifareApplication functions are tied to mifare_clasic_* ones and
    some refactoring is required to have a consistent API.
[ ] Refactor examples and have consistent behavior.
    Dump to stdout unless -o is specified;
    Read from stdin unless a file is specified;
    Humanize dumps with a -h flag;
    Target aquisition is the same in all examples;