ZlpDirectoryInfo and CreateSubdirectory method

[Vahid Nasiri]

Hi, ZlpDirectoryInfo.CreateSubdirectory method is missing.
It can be implemented this way:

        public ZlpDirectoryInfo CreateSubdirectory(string name)
        {
            var path = ZlpPathHelper.Combine(_path, name);
            ZlpIOHelper.CreateDirectory(path);
            return new ZlpDirectoryInfo(path);
        }

[Uwe Keim]

I've implemented this. Will update soon.