Add gd::FileStream (#312)

* Fix unicode paths on Windows for XML files
* Add a fstream equivalent that supports gd::String paths (with characters outside the current codepage on Windows)
* Add a sf::InputStream subclass for the same purpose
* Use gd::FileStream in DatFile and ResourcesLoader
* Replace remaining i/ofstream with gd::FileStream

Core/GDCore/IDE/AbstractFileSystem.cpp

@@ -5,6 +5,7 @@
  */
 
 #include "GDCore/String.h"
+#include "GDCore/Tools/FileStream.h"
 #include <algorithm>
 #include "AbstractFileSystem.h"
 #include "GDCore/CommonTools.h"
@@ -108,7 +109,7 @@ gd::String NativeFileSystem::GetTempDir()
 
 bool NativeFileSystem::WriteToFile(const gd::String & filename, const gd::String & content)
 {
-    std::ofstream file( filename.ToLocale().c_str() );
+    gd::FileStream file( filename );
     if ( file.is_open() ) {
         file << content.ToUTF8();
         file.close();
@@ -120,7 +121,7 @@ bool NativeFileSystem::WriteToFile(const gd::String & filename, const gd::String
 
 gd::String NativeFileSystem::ReadFile(const gd::String & file)
 {
-    std::ifstream t(file.ToLocale().c_str());
+    gd::FileStream t(file);
     std::stringstream buffer;
     buffer << t.rdbuf();
     return gd::String::FromUTF8(buffer.str());