Packages generation default to specific Python version

[artemdinaburg]

Our binary package generation defaults to a specific Python version. Is there a way to make it more generic? It's fine if there is not, in that case lets officially document a specific python revision.

Example:

dpkg -c anvill-0.1.39.be24fd5-x86_64.deb
... skip some output ...
rwxr-xr-x root/root         0 2021-02-22 16:55 ./usr/local/lib/python3.8/
drwxr-xr-x root/root         0 2021-02-22 16:55 ./usr/local/lib/python3.8/dist-packages/
drwxr-xr-x root/root         0 2021-02-22 16:55 ./usr/local/lib/python3.8/dist-packages/anvill/
...