Clean up coverage writing

[jspaaks]

coverage was written into various places, this PR cleans that up. Everything is now under /coverage, like so:

coverage/
├── .coverage
├── coverage.xml
├── htmlcov
│   ├── coverage_html.js
│   ├── fairtally_check_py.html
│   ├── fairtally_cli_py.html
│   ├── fairtally___init___py.html
│   ├── fairtally_redirect_stdout_stderr_py.html
│   ├── fairtally_utils_py.html
│   ├── fairtally___version___py.html
│   ├── favicon_32.png
│   ├── index.html
│   ├── jquery.ba-throttle-debounce.min.js
│   ├── jquery.hotkeys.js
│   ├── jquery.isonscreen.js
│   ├── jquery.min.js
│   ├── jquery.tablesorter.min.js
│   ├── keybd_closed.png
│   ├── keybd_open.png
│   ├── status.json
│   └── style.css
└── README.md

The configuration is now more explicit, in /.coveragerc

[jspaaks]

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