Constructor should encode Unicode input as Punycode

[ypcrts]

Goal: implement RFC3492 https://tools.ietf.org/html/rfc3492

In the constructor, Unicode input should be encoded as Punycode.

TODO:

• [ ] Use punycode from the python3 codecs library. https://docs.python.org/3/library/codecs.html
• [ ] Investigate whether this will work in python 2.7, if not devise a plan