Removed 'using namespace std;' from documentation examples

#include <TNL/String.h>

using namespace TNL;

using namespace std;

int main()

{

    file >> restoredString;

    file.close();

    cout << "restored string = " << restoredString <<endl;

    std::cout << "restored string = " << restoredString << std::endl;

}

#include <cuda.h>

using namespace TNL;

using namespace std;

int main()

{

   cudaFree( deviceArray );

   delete[] hostArray;

}

#include <TNL/File.h>

using namespace TNL;

using namespace std;

int main()

{

#include <iostream>

#include <TNL/FileName.h>

using namespace TNL;

using namespace std;

int main()

{

      std::cout << fileName.getFileName() << std::endl;

   }

}

#include <TNL/Containers/StaticVector.h>

using namespace TNL;

using namespace std;

int main()

{

      std::cout << fileName.getFileName() << std::endl;

   }

}