Allow to work with UTF-8 characters

I know that this is not the most popular library ever, but sadly I had a pleasure to implement extension for IDN domain names using epp-rtk. The issue is that the code as it is right now is capable of working with ASCII names, but not with UTF-8 ones. I had to implement extension which is sending U-Labels as one of the nodes and had wasted enough time working out where was the issue with encoding, while it ended being in the epp-rtk library itself. 

It might not be useful to anybody, but hey, it never hurts squashing bugs:)