Added ConfigManager to preserve some values. Fixes #221

Well, mkstemp() is not what I want to use. ConfigManager should create a config file and I want to check whether it created the file successfully. Mkstemp() creates a file, but all I want is to get some filename which is free and safe to use. Mktemp() is the function which does it. I see it is marked as deprecated, but I currently don't know any different good solution. So I hope using mktemp() won't cause any problems.