restructure the repository and add testing

[zivy]

First step towards a nice Python package, via the PR from @blowekamp.

Complete the process and create the directory structure which is commonly used for Python packages, see packaging tutorial.

Also, add testing and a bit of cleanup (e.g. here).

[blowekamp]

The configuration of the pyproject.toml is complete. It is written so support a single installed python executable in the python packaging system.

[jcfr]

@blowekamp @dave3d I think this can be closed as well.

Testing was introduced in the following pull requests:

• WIP: initial testing checkin #11
• run test on itself; allow multple suffixes #12

Packaging support was introduced in this pull request:

• Make package #7