ACR122 devices support enhancements.

- Add driver agnostic nfc_pick_device(), nfc_list_devices();
  - New API function: nfc_list_devices();
  - PCSC Context sharing for acr122 driver;
  - List all devices in nfc-list(1);
  - Various code fixes and cleanup;
  - Remove warnings when compiling;
  - Merge r191:199 from trunk \_°< Coin!

src/lib/chips/pn53x.c

@@ -21,6 +21,7 @@
  * @brief PN531, PN532 and PN533 common functions
  */
 
+#include <string.h>
 #include <stdio.h>
 
 #include "pn53x.h"