Flush the input buffer on posix and windows.

def input_flush():
    """Flush the input buffer on posix and windows."""
    try:
        import sys, termios  # noqa
        termios.tcflush(sys.stdin, termios.TCIFLUSH)
    except ImportError:
        import msvcrt
        while msvcrt.kbhit():
            msvcrt.getch()