Enhance error handeling.

- New API functions: nfc_strerror(), nfc_strerror_r() and nfc_perror();
  - Drivers now have a reference to chips callback methods;
  - Rename -pn53x_err2string to pn53x_strerror and add it to pn53x_callbacks_list.

include/nfc/nfc-types.h

@@ -93,6 +93,15 @@ typedef struct {
   uint32_t uiBusIndex;
 } nfc_device_desc_t;
 
+/**
+ * @struct chip_callbacks
+ * @brief Functions for chip specific functions.
+ */
+struct chip_callbacks {
+    /** Error lookup */
+    const char* (*strerror) (const nfc_device_t *pnd);
+};
+
 /**
  * @struct driver_callbacks
  * @brief Generic structure to handle NFC device functions.
@@ -100,6 +109,8 @@ typedef struct {
 struct driver_callbacks {
   /** Driver name */
   const char* acDriver;
+  /** Chip specific callback functions */
+  const struct chip_callbacks *pcc;
   /** Pick devices callback */
   nfc_device_desc_t *(*pick_device)(void);
   /** List devices callback */

include/nfc/nfc.h

@@ -78,6 +78,11 @@ NFC_EXPORT bool nfc_target_send_bits(nfc_device_t* pnd, const byte_t* pbtTx, con
 NFC_EXPORT bool nfc_target_send_bytes(nfc_device_t* pnd, const byte_t* pbtTx, const size_t szTxLen);
 NFC_EXPORT bool nfc_target_send_dep_bytes(nfc_device_t* pnd, const byte_t* pbtTx, const size_t szTxLen);
 
+/* Error reporting */
+NFC_EXPORT const char *nfc_strerror (const nfc_device_t *pnd);
+NFC_EXPORT int nfc_strerror_r (const nfc_device_t *pnd, char *pcStrErrBuf, size_t szBufLen);
+NFC_EXPORT void nfc_perror (const nfc_device_t *pnd, const char *pcString);
+
 /* Special data accessors */
 NFC_EXPORT const char* nfc_device_name(nfc_device_t* pnd);