MultiBar does not honour custom handle on Windows

Hello,

I am using a "/dev/null" like handle when my application is in quiet mode to hide the progress bar.

On unix, `tty::move_cursor_up` returns a string which is output to the handle.
On windows,` tty::move_cursor_up` print to the console and return an empty string whatever the handle is, making my trick to have a quiet mode totally failing.

I do not know if the windows code could be fixed easily. Otherwise what about introducing a quiet mode ?