Error Handling and Protocol Enhancements

[gbakeman]

With these changes, my aim is to make the user experience more friendly during the connection and authentication steps. I've also tried to make our jobs as programmers a little easier. A summary of the changes:

• Added an enumeration of possible NUT protocol responses, and a very basic function that will parse a response string into an enum value. More work to come, if it would be helpful.
• Modified a log string to also print out what the error is specifically, to help the user understand what the problem is.
• Modified the username portion of the authentication function to make use of the new responses enum, and handle another case of failure. I also removed the call to reconnect if there's an exception, since I think we'd want the process to hard-fail if there's any issue with authentication. This should hopefully help with error notification spam.

I hope this is beneficial to you!

[gawindx]

It seems correct to me, I validate.