Update tooling and tests

[mwchase]

The only strictly necessary change here is the updates to the test file, which address #10. However, I first added some configuration files to allow for the following things without explicitly executing setup.py:

• Building via general PEP 517 frontends, such as https://github.com/pypa/build
• Running tests across multiple Python versions, without having to handle the virtual environments or installs explicitly

[vzool]

+1