Punycode module currently doesn't support mixed-case annotation

[bivens-dev]

As a part of the effort towards Issue #6 we are bug for bug compatable with the Punycode.js library that was used as the basis for the code in this project dealing with Punycode.

The original bug as outlined here: mathiasbynens/punycode.js#3 comes up in one of our tests that says:

As there's no way to do it in JavaScript, Punycode.js doesn't support mixed-case annotation (which is entirely optional as per the RFC). So, while the RFC sample string encodes to: b1abfaaepdrnnbgefbaDotcwatmq2g4l Without mixed-case annotation it has to encode to: b1abfaaepdrnnbgefbadotcwatmq2g4l

I'm assuming that Dart probably doesn't have the same limitations that caused this bug in the first place but it is something that would need further investigation which probably isn't going to happen anytime soon.