Github CI running clean on linux/Windows

Hi trn fans,

It's been a while since I poked at this code, so I came back to it
over the weekend and made the following progress:

- Github CI (continuous integration) builds running green on linux & Windows
  <https://github.com/LegalizeAdulthood/trn/actions>
- All tests are passing on Windows
- 4 tests on linux report about a leaked mock from gmock
  I've seen this occasionally at work and I believe it to be either a
  bug in gmock when a method returns a mock by shared_ptr or I'm not
  using gmock correctly in this scenario [always possible :)].
  Interestingly enough, the "leaked mock" is only reported on linux.
  For now I've suppressed the 4 tests on linux in the CI build.  The
  logic exercised actually passes, it's just marked as a failure
  because gmock complains about the "leaked" mock.
- CMakePresets.json added to simplify configure/build/test workflows
- Source files moved into subdirectories;
  Now the main directory doesn't contain a giant pile of files.
- .editorconfig support added

I think the code should be working reasonably well at this point, but
I need to do some integration testing.  In order for other people to
assist with that, I'm going to work on creating installers with CPack
next.

Then releases can start being posted to github and people can try
things out and give me feedback in an orderly manner.
-- 
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  Legalize Adulthood! (my blog) <http://LegalizeAdulthood.wordpress.com>