Add support for Python 3.5

[PeterHamilton]

With the recent release of Python 3.5, many Python developers are upgrading to a version of Python not officially supported by PyKMIP. Since PyKMIP already supports Python 3.3 and 3.4, adding official support for 3.5 should be trivial.

[rellerreller]

I hope it's trivial. 👍

[PeterHamilton]

Unfortunately it's not. It took me a little while to trace the issue but there's a weird error that occurs when you attempt to run py35 in tox when you have enum34 installed in older versions of Python. It has something to do how virtualenv works internally, which tox uses. Lots of nastiness.

This was the initial issue on the problem last year: pypa/virtualenv#763. It was supposed to be fixed, so either the issue's reappeared or I'm not doing the right thing in the right way. Apparently there's an ongoing effort to rewrite the bulk of virtualenv to play nice with different interpreters/platforms/environments/etc, so that may fix things eventually.

It also turns out that Travis has had/has issues with 3.5: travis-ci/travis-ci#4794.

Needless to say, there are issues with just adding 3.5 support. I'm leaving this issue open for now, as a todo, but I won't address it for a while.

[PeterHamilton]

I added Python 3.5 support with PR #203, so this is done now.