remove dependencies unittest2 and future

[dyollb]

Fixes #77.

Remove dependency to unittest2 and future.

• future isn't used anywhere in the code
• unittest2 is used only in one test

I also slightly modernized the package. All configuration settings are now in a pyproject.toml.

I ran the tests locally and they pass:

[dyollb]

Also removed setup.cfg. It was specifying the description (readme file), but this is already included in the pyproject.toml.

[MattTheCuber]

A recent vulnerability was found in the future package as well: GHSA-xqrq-4mgf-ff32

This PR (and a release) would resolve this security issue.

[MattTheCuber]

If the unittest changes need further review and/or testing, let me know so that I can open a PR that simply removes the future package dependency as this is a critical vulnerability.