bump version -> 0.3.2

replace setup.py etc. with pyproject.toml

make compliant with REUSE spec

remove use of pydocstyle (no longer maintained)

remove use of pytest-xdist

remove use of coverage

The hypothesis tests time out when recording coverage.

remove use of tox and pyenv

minor formatting fix with black

makefile: add task to upload readme to sourcehut

docs cleanup

new builds.sr.ht script

Remove builds.sr.ht script

Update CI script to stay on debian/buster

debian/stable is now bullseye, which doesn't provide Python 2 packages.

Update links for issues/PRs in Contributing docs

Update changelog

Add docstrings; check with pydocstyle

Add flake8 plugin to check for naming convention

Add build script task to render & upload readme

Sourcehut only displays `README` or `README.md` by default.
Rst-formatted docs need to be compiled to HTML manually:
https://man.sr.ht/git.sr.ht/#setting-a-custom-readme

Replace Travis CI with builds.sr.ht script

Update latest supported version to Python 3.9