Use the documented 5 line prolog in every sample application. Tidy up sample prologs and header code.

samples/stringto-test.cpp

@@ -21,7 +21,6 @@
  */
 
 #include <exiv2/exiv2.hpp>
-
 #include <iostream>
 #include <iomanip>
 
@@ -60,6 +59,9 @@ int main()
 {
     Exiv2::XmpParser::initialize();
     ::atexit(Exiv2::XmpParser::terminate);
+#ifdef EXIV2_ENABLE_BMFF
+    Exiv2::enableBMFF();
+#endif
 
     std::cout << std::setfill(' ');