versioneer and docker

[codl]

this 3c372a2afb3a3d17d357ae79789633b6e2132189 is gross

apparently versioneer replaces version.py with a static version when a source distribution is generated, so maybe the way to go is to

• make building an sdist possible (is it already possible?)
• generate that sdist in a docker stage and install it in another

which would still mean sending .git to docker which is still gross, but at least it doesn't end up in the final image or any of its ancestors