Support ELLIPSIS marker

[ArneBachmannDLR]

With using doctest you can use ... to mean regex-like .* catchall.
When converting to logot I stumbled upon AssertionError: Not logged: until realizing I had ... inside the expected output.

[ArneBachmannDLR]

Just found out about https://logot.readthedocs.io/latest/log-message-matching.html which wasn't clear from the Github README alone, that solved my issue. Above idea may still be interesting.

[etianen]

I've flirted with the idea of supporting alternate match syntax (see #31). If there was demand for this, I'd consider making a generic mechanism to match using other syntaxes, of which ... would be a good option.

I'm marking this idea as wontfix for now, as there are no immediate plans. If other people stumble upon this issue and think it would be worthwhile, however, feel free to comment and we can think about ways it could be implemented! ❤️

Meanwhile, I've updated the README with some deep links to the logot docs (see #125). Hopefully this will help other people find the log message matching docs in future! 🙇