update readme/project setup for modern pip/tox and remove setuptools

[RonnyPfannschmidt]

addresses part of #93

[Goldziher]

Sorry for jumping in :), would you like my help setting up a github pipeline? We have good tooling in snok for using poetry actions and a setup that makes life very easy when publishing.

Also - a lot of experience with pre-commit configs and setup, see this: https://github.com/snok/drf-openapi-tester for example, and this for the github poetry: https://github.com/snok/install-poetry

[RonnyPfannschmidt]

@Goldziher i wouldn't mind some help

currently i avoid poetry as it breaks a number of workflows for me (including foreign editable install, setuptools_scm integration and a few others)

currently have a spike at work for something else, i'll have some more time next week