Fixed: Added buffering for open function to improve writing to usb stick on windows.
    .For a 30M file, it decreses time for f_output.write()(less then 1 sec),
     but takes more time for f_output.close()(about 15s). Anyway, It save about 3s
     compring to previous release.
Improve writing to USB stick and add homework containning some algorithm code.