Fix issue #106

[tmuaz]

See #106 for details.

I've just swapped out Arc<Mutex<Cursor<Vec<u8>>>> for Arc<Mutex<Vec<u8>>>.

This doesn't seem to break anything but I'm assuming Cursor was being used for a reason and it does take away that functionality.

[tmuaz]

Simply resetting the buffer position to 0 after a clear also seems to work. I'm just not entirely as to why this doesn't trigger in Startup but triggers in Update.

    {
        let buffer = buffer.get_mut();
        for line in buffer.lines().map_while(Result::ok) {
            // assert_eq!(line.trim_start_matches('\0').len(), line.len());
            console_lines.write(PrintConsoleLine { line });
        }
        buffer.clear();
    }
    buffer.set_position(0);
}