Second part of error handling.

- Define two sets of DE<FOOBAR> macros: the first one for 'generic' errors
  which could be encountered regardless of the NFC device the library is acting
  with (0xX000), and ont set for device-dependant errors (0x0X00).
- Make some more functions accept a nfc_device_t* as first argument to have
  access to the iLastError;
- Reset errors when entering public API functions;
- Save errors when applicable;
- Distinguish system-level errors (e.g. I/O error) and operational errors (the
  PCD returns an unexpected value);
- Minor tweaks.

Update issue 65
Status: Feedback

New review:
Owner: rconty@il4p.fr
Cc: rtartiere@il4p.fr
Summary: Review the error-handling code.
Branch: /branches/libnfc-error-handling

For this development, a strong emphasis has been set on making changes that
will not go through our way on the way to libnfc-1.6+.  For this reason, some
constructs are not natural (e.g. error codes defined in two different places),
please keep this in mind when reviewing.

include/nfc/nfc-types.h

@@ -69,7 +69,14 @@ typedef struct {
   bool bPar;
 /** The last tx bits setting, we need to reset this if it does not apply anymore */
   uint8_t ui8TxBits;
-/** Last error reported by the PCD / encountered by the PCD driver */
+/** Last error reported by the PCD / encountered by the PCD driver
+ * MSB       LSB
+ *  | 00 | 00 |
+ *    ||   ||
+ *    ||   ++----- Chip-level error (as reported by the PCD)
+ *    |+---------- Driver-level specific error
+ *    +----------- Driver-level general error (common to all drivers)
+ */
   int iLastError;
 } nfc_device_t;