#107 Win32 Progress Flush Fix

[MuldeR]

On the Windows platofrm it is required to explicitly flush the STDERR after printing the progress message. Otherwise, the parent process does NOT get the progress until either the buffer is flushed implicitly (because it happens to exceeds its limits) or the SoX process terminates. So, if we want to process progress updates in "real time", we need explicit flushing!