Adding S/M support to libmrtd

If you've now thought about something sexual, I have to disappoint you. At least this time I'm talking about ISO/IEC 7816-4 SM (secure messaging) ;) For those not familiar with cryptographic smart cards: SM is similar to what SSL/TLS do for TCP.

The code for re-formatting the 7816-4 APDU's into further levels of ASN.1, including padding rules, encrypting, authentication, ... has become quite complex. It's also not finished yet, and I already fear testing/debugging of that beast.