TIL! Using the existence of obscure member sys._MEIPASS, I can detect if
we're running from a bundled PyInstaller binary, versus running from Python
directly.
Add schema.yaml to the datas of the PyInstaller spec. Then, if the
-/--schema flag is given, use it, and if it's not given, default to the
built-in one if we're running from a bundled binary, or fall-through to
./schema.yaml in other cases.
This avoids the need for config/schema.py as a carbon-copy of the schema,
slick!
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