Credentials Library

This is a fast portable C library which provides both high-level and
low-level (cryptographic) credential operations.


API Overview:
 - credential.h provides the high-level credential operations with integrated 
     card interaction.
 - credential_terminal.h provides the high-level credential operations without
     card interaction, this allows the developer to handle the communication.
(- credential_types.h provides the data types shared by both high-level APIs.)

 - credential_crypto.h provides the low-level cryptographic operations.
 - credential_card.h provides the low-level APDU processing operations, that is 
     the generation of commands and translation to and from internal data types.