add some Doxygen documentation.

include/nfc/nfc-emulation.h

@@ -17,6 +17,11 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>
  */
 
+/** 
+ * @file nfc-emulation.h
+ * @brief Provide a small API to ease emulation in libnfc
+ */
+
 #ifndef __NFC_EMULATION_H__
 #define __NFC_EMULATION_H__
 
@@ -30,13 +35,20 @@ extern  "C" {
 struct nfc_emulator;
 struct nfc_emulation_state_machine;
 
-
+/**
+ * @struct nfc_emulator
+ * @brief NFC emulator structure
+ */
 struct nfc_emulator {
   nfc_target *target;
   struct nfc_emulation_state_machine *state_machine;
   void *user_data;
 };
 
+/**
+ * @struct nfc_emulation_state_machine
+ * @brief  NFC emulation state machine structure
+ */
 struct nfc_emulation_state_machine {
   int (*io)(struct nfc_emulator *emulator, const uint8_t *data_in, const size_t data_in_len, uint8_t *data_out, const size_t data_out_len);
   void *data;