Catch2 XML reporter does not output sections properly

[cschreib]

Reported in #169.

Without these changes CI and IDEs work ok, but failures in a section just fail the whole test. When we were using Catch2 a failure would be specific to a section allowing us to quickly drill down to the problem. So looking into the difference it is just the lack of section output in the "high" verbosity mode. Catch2 outputs section XML data by default.

It was fairly easy to make it work with basic testing, pass and fail. There are more complex edge cases around skips, nested sections, exceptions being thrown, and different verbosity levels. I am still ironing those out and need to make sure there is testing for it all.