Support venv and use of github actions for contributors

[MusicalNinjaDad]

Resolves #1109

The current .gitignore, setup.py and test.yml are focussed on a specific development set up. These changes support a few additional development setup preferences without breaking anything. (Do no harm):

• Using pythons venv virtual environments,
• using editors other than vim
• debugging (via) tests,
• leveraging github actions for regression testing,
• visualising code coverage results on codecov.io

Each of these adjustments do no harm, and are individually committed to allow for cherry-picking if there is something you do not like.

If these changes are not integrated into the main codebase then any PRs raised by someone who has made a similar adjustment to support their environment will either silently include them or need rebasing before raising and then be prone to error due to a large number of changes suddenly being present in working tree, regression testing not executing etc. on the final code included in the PR.

A note on codecov.io - the action will do nothing if the repo is not previously linked, so there is no data uploaded etc. unless the repo owner has specifically set this up in advance. I.e. no harm in the action being present at the end of the pipeline.