less structs and defines publicly exposed

- nfc_device is now an opaque type;
 - PN53x specific errors are not public anymore;
 - nfc_device_name() renamed to nfc_device_get_name() for the sake of consistency;
 - examples/*, utils/* uses the new nfc_device_get_name() function instead of access directly to struct's content;
 - new error defined: NFC_ERFTRANS for notifying about RF transmission error, its used by mifare.c to detect permissions error on mifare;
 - drivers initiator_transceive_bytes() function now returns libnfc's error code on failure (<0), and received bytes count on success (>=0);
 - remove some unused errors.

libnfc/chips/pn53x-internal.h

@@ -299,6 +299,34 @@ typedef struct {
 #define PN53X_SFR_P7CFGB 0xFFF5
 #define PN53X_SFR_P7 0xFFF7
 
+/* PN53x specific errors */
+#define ETIMEOUT	0x01
+#define ECRC		0x02
+#define EPARITY		0x03
+#define EBITCOUNT	0x04
+#define EFRAMING	0x05
+#define EBITCOLL	0x06
+#define ESMALLBUF	0x07
+#define EBUFOVF		0x09
+#define ERFTIMEOUT	0x0a
+#define ERFPROTO	0x0b
+#define EOVHEAT		0x0d
+#define EINBUFOVF	0x0e
+#define EINVPARAM	0x10
+#define EDEPUNKCMD	0x12
+#define EINVRXFRAM	0x13
+#define EMFAUTH		0x14
+#define ENSECNOTSUPP	0x18	// PN533 only
+#define EBCC		0x23
+#define EDEPINVSTATE	0x25
+#define EOPNOTALL	0x26
+#define ECMD		0x27
+#define ETGREL		0x29
+#define ECID		0x2a
+#define ECDISCARDED	0x2b
+#define ENFCID3		0x2c
+#define EOVCURRENT	0x2d
+#define ENAD		0x2e
 
 #ifdef LOGGING
 static const pn53x_register pn53x_registers[] = {