Convert by value passing of nfc_target to pointer for str_nfc_target and nfc_initiator_target_is_present

This becomes more consistent with all other pass by pointer of most structures.
Additionally, this should lessen stack memory usage, as building strings with str_nfc_target would push the target (283 bytes) plus then a copy of the info objects (up to 275) onto the stack as it dives into the sprintf functions.

Lastly, this makes my attempt at a .NET wrapper easier, as I can make passing by pointer work, but passing by value seems to bomb on the interop right now.

examples/nfc-dep-initiator.c

@@ -103,7 +103,7 @@ main(int argc, const char *argv[])
     nfc_exit(context);
     exit(EXIT_FAILURE);
   }
-  print_nfc_target(nt, false);
+  print_nfc_target(&nt, false);
 
   printf("Sending: %s\n", abtTx);
   int res;

examples/nfc-dep-target.c

@@ -126,7 +126,7 @@ main(int argc, const char *argv[])
   signal(SIGINT, stop_dep_communication);
 
   printf("NFC device will now act as: ");
-  print_nfc_target(nt, false);
+  print_nfc_target(&nt, false);
 
   printf("Waiting for initiator request...\n");
   if ((szRx = nfc_target_init(pnd, &nt, abtRx, sizeof(abtRx), 0)) < 0) {

examples/nfc-emulate-tag.c

@@ -266,7 +266,7 @@ main(int argc, char *argv[])
   */
 
   printf("%s will emulate this ISO14443-A tag:\n", argv[0]);
-  print_nfc_target(nt, true);
+  print_nfc_target(&nt, true);
 
   // Switch off NP_EASY_FRAMING if target is not ISO14443-4
   nfc_device_set_property_bool(pnd, NP_EASY_FRAMING, (nt.nti.nai.btSak & SAK_ISO14443_4_COMPLIANT));

examples/nfc-poll.c

@@ -137,7 +137,7 @@ main(int argc, const char *argv[])
   }
 
   if (res > 0) {
-    print_nfc_target(nt, verbose);
+    print_nfc_target(&nt, verbose);
   } else {
     printf("No target found.\n");
   }