wide string: To{W,}String: provide overload for rvalue references

src/utility/wide_string.h

@@ -21,10 +21,19 @@
 #ifndef NCMPCPP_UTILITY_WIDE_STRING_H
 #define NCMPCPP_UTILITY_WIDE_STRING_H
 
-#include <string>
+#include <string> // include before boost to compile on MACOSX
+#include <boost/locale/encoding_utf.hpp>
 
-std::string ToString(const std::wstring &ws);
-std::wstring ToWString(const std::string &s);
+template <typename StringT>
+std::string ToString(StringT &&s)
+{
+	return boost::locale::conv::utf_to_utf<char>(std::forward<StringT>(s));
+}
+template <typename StringT>
+std::wstring ToWString(StringT &&s)
+{
+	return boost::locale::conv::utf_to_utf<wchar_t>(std::forward<StringT>(s));
+}
 
 size_t wideLength(const std::wstring &ws);
 void wideCut(std::wstring &ws, size_t max_length);