consider adding a changelog

[Thomas Gilgenast]

could be roughly something like this:

https://keepachangelog.com/en/1.0.0/

we try to record changes in commit messages, but having a place where you can see the important changes at-a-glance seems much much better than scrolling through commit logs no one will read anyway

[Thomas Gilgenast]

added changelog, first wave of heatmap speed improvements

closes #28, closes #47, fixes #56

updated flake8 config, simplified .gitignore

→ <<cset af833d51b475>>