Usage of EXIT_SUCCESS/FAILURE instead of hard-coded values

samples/xmpprint.cpp

@@ -16,7 +16,7 @@ int main(int argc, char** argv) {
   try {
     if (argc != 2) {
       std::cout << "Usage: " << argv[0] << " file\n";
-      return 1;
+      return EXIT_FAILURE;
     }
 
     auto image = Exiv2::ImageFactory::open(argv[1]);
@@ -42,9 +42,9 @@ int main(int argc, char** argv) {
 
     Exiv2::XmpParser::terminate();
 
-    return 0;
+    return EXIT_SUCCESS;
   } catch (Exiv2::Error& e) {
     std::cout << "Caught Exiv2 exception '" << e << "'\n";
-    return -1;
+    return EXIT_FAILURE;
   }
 }