Update for python 3.8

[noahp]

Thank you for making this software, and making the source available!

This patch has a collection of modifications:

• update to be compatible with python 3.8
• update the tests to include the file list header
• update setup.py (version number bump and add python2.7 + python3.8
  classifiers)
• add a dockerfile to preserve the testing environment, using tox as the
  test runner
• converted the README to Markdown and added the extension so Github
  renders it
• update .gitignore for the tox temporary files

The motivation for this patch-

Ubuntu 20.04 no longer has dtrx in the PPA's, I think because it only
supported python 2. I checked the pypi.org page for dtrx, but I think it
was migrated from pypi.python.org, and the package page is empty.

This patch should be enough to deploy an update to pypi.org, to make the
tool available to anyone via pip install dtrx. I've updated the readme
with that information too (and it may be worth adding a badge).

I've deployed a test version of this path to
https://pypi.org/project/dtrx-noahp/

[noahp]

If we wanted to test on more python versions (3.6, 3.7, etc) we could use pyenv to install them to the docker image: https://github.com/pyenv/pyenv

[ikerexxe]

I've tested it in Fedora 31 and it works correctly.

Moreover, the problem that I had in this same system with brettcs' master related with python has been solved. I think that this problem was related with the usage of some python 2 dependency that has already been removed in latest versions of Fedora.

[AlanRosenthal]

@brettcs any thoughts on merging this PR?

[pizzadude]

Tested and works fine in Fedora 32.

[ChrisJefferson]

Hi @noahp (not sure the best other way of contacting you), I have recently acquired control of dtrx on pypi, so I'd be happy to talk to you about getting this officially released. Can you email me at chris@bubblescope.net ?

[noahp]

FYI: this patch is included in the fork at https://github.com/dtrx-py/dtrx , and deployed to PyPi at https://pypi.org/project/dtrx/ . Closing this PR.