Build Improvements and Python 2.6 Support Dropped

[opalmer]

This PR was created to get the build working again, replace old libraries and make other small improvements. A full list of changes can be found in changelog.rst. The most notable change introduced in this PR is in a4ea830

remove Python 2.6 from build

There are several dependencies which no longer support
Python 2.6 including the wheel library. Twisted itself
also no longer supports Python 2.6. Finally, official support
for the version ended back in 2013 and several major operating
systems do not use it as their default version.

At this time pywincffi still works with Python 2.6 but some of the libraries we depend on do not.

[codecov-io]

Codecov Report

Merging #126 into master will not change coverage.
The diff coverage is 100%.

[opalmer]

@rodrigc please take a look. I was looking at #125/#124/#123/#122 and found the build was broken and needed some updates. I mainly wanted to run this PR by you to make sure dropping 2.6 would work for Twisted (last I recall, it should because the later versions no longer support 2.6?).

I have not had a chance yet to look into what's going to be required to support the functions you requested but this PR will have to merge first before I can start.

Some additional requests and questions for you:

• Would you mind updating the issues you filed with examples in Twisted where the functions are being called? That can help write tests and would give me an idea of how those functions are currently being used.
• Do you have a preference in terms of which of the issues you filed I should be looking into first?

[rodrigc]

Twisted 15.4.0 was the last version to support Python 2.6: https://github.com/twisted/twisted/blob/trunk/NEWS.rst#twisted-core-1540-2015-09-04

so if you want to drop Python 2.6 support, that is fine.

[rodrigc]

In terms of examples of the API's I mentioned, you can search the Twisted codebase for where they are used. They are in different classes in Twisted.