Added documentation, with change logs managed by towncrier

[andy-maier]

For looking at the documentation, run make builddoc with this PR checked out and open build_docs/index.html in a browser.

A corresponding project on ReadTheDocs has been created, and the first documentation should be built there when this PR is merged: https://zhmc-log-forwarder.readthedocs.io/en/latest/

[coveralls]

Pull Request Test Coverage Report for Build test-89

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 24.061%

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Totals
Change from base Build test-88:	0.0%
Covered Lines:	141
Relevant Lines:	586

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💛 - Coveralls