github actions no longer supports python 3.4

This is an updated revision of pull requests #206 and #524

In a project with all lines indented 4 spaces, I noticed pycodestyle was
not catching code that was accidentally indented two levels (8 spaces).
The over indentation was unintended and can be caught during static
analysis.

Fixes #430

The nose project has ceased development. The last commit is from Mar 3,
2016. From their docs page:

https://nose.readthedocs.io/

> Note to Users
>
> Nose has been in maintenance mode for the past several years and will
> likely cease without a new person/team to take over maintainership.
> New projects should consider using Nose2, py.test, or just plain
> unittest/unittest2.

For details on the new PyPI, see the blog post:

https://pythoninsider.blogspot.ca/2018/04/new-pypi-launched-legacy-pypi-shutting.html

Python 2.6 an 3.3 are end of life. They are no longer receiving bug
fixes, including for security issues. Python 2.6 went EOL on 2013-10-29
and 3.3 on 2017-09-29. For additional details on support Python
versions, see:

https://devguide.python.org/#status-of-python-branches

Removing support for EOL Pythons will reduce testing and maintenance
resources. Removed all workarounds for older Pythons.

Updated trove classifiers and documentation to better communicate
supported Python versions.

Additionally, pass python_requires argument to setuptools. Helps pip
decide what version of the library to install.

https://packaging.python.org/tutorials/distributing-packages/#python-requires

> If your project only runs on certain Python versions, setting the
> python_requires argument to the appropriate PEP 440 version specifier
> string will prevent pip from installing the project on other Python
> versions.

https://setuptools.readthedocs.io/en/latest/setuptools.html#new-and-changed-setup-keywords

> python_requires
>
> A string corresponding to a version specifier (as defined in PEP 440)
> for the Python version, used to specify the Requires-Python defined in
> PEP 345.

Can now use more modern Python syntax including dictionary comprehension
as well as more generators.

Closes #755