This can also demonstrate how they can be used with the new shiny vis_expect function from visdat.

I've searched quite hard but can't find detail on the differences implied by the different mimic options. There are many references to mimic throughout the codebase, but I wonder if there was a single list or table of the differences implied?

todo

1. Dockerfile.pybase builds the eltonlaw/pybase image which sets up the python environments. Add stuff to install pypy here.
2. Dockerfile builds the impyute image which installs dev requirements and installs impyute. Add stuff to install impyute into the new pypy enviroment.
3. Update README.rst to support pypy
4. Add $ docker run impyute pypy -m pytest to the `test