Fill-in the pyproject.toml

[Florents-Tselai]

Here's an attempt to $subject, with a pretty standard approach.

• I've set the version to be picked up from __init__.py/__version, but I'm not sure if there's any version tagged;
  If not, I think it'd be a good idea.
• Also haven't filled the author/email details.

Also thought of adding some boilerplates for tests, but leaving it that for later.