Get PyPy to work for fun

[jamespfennell]

Would be interesting to get a Transiter Docker image based on PyPy (currently only Python 3.6 is supported). I tried, and failed though there seemed to be a single problem and thus hope. What I needed to do:

• Remove black and possibly twine from dev-requirements.txt.
• Change references in the Docker file from python to pypy3.
• Run pip install dataclasses to get the Python 3.6 version of dataclasses.

What failed:

• The default Postgres driver doesn't work on PyPy. Need to use another driver. Because of this, would need to benchmark performance.

[jamespfennell]

For the dataclasses requirement, I see this in dataclasses-json's setup.py:

    install_requires=[
        'dataclasses;python_version=="3.6"',

[jamespfennell]

Won't fix