Use pyproject.toml

[akaszynski]

I think that the community at large is shifting towards pyproject.toml, and our template should have this as a starting point.

@da1910 and @MaxJPRey, would be excellent if you guys could get to this at some point in the near future.

[greschd]

When using pyproject.toml, do we want to use flit as build backend, or something else? I anyway need to do this for ACP, so there's no additional effort in doing it here directly.

[MaxJPRey]

@greschd Let's use flit for now. Potentially, we can switch latter to Poetry. It seems that flit is the simplest way for packaging.

[akaszynski]

Resolved in #6 by using poetry. We can change back to flit as needed.