The error messages for a theme that failed to be deserialized (or otherwise failed to load) were covered up by the context/with_context calls: * The log message for a bad theme configured in config.toml would only say "Failed to deserilaize theme" * Selecting a bad theme via :theme would show "Theme does not exist" With these changes, we let the TOML deserializer errors bubble up, so the error messages can now say the line number of a duplicated key - and that key's name - when a theme fails to load because of a duplicated key. Providing a theme which does not exist to :theme still gives a helpful error message: "No such file or directory."