Raspi-door

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* Fixed handling of null wind chill factor

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* Fixed weather service to properly use the `tz` configuration

* Added OpenWeatherMap.org configurations to control tomorrow's
forecast:

* forecast.tomorrow.offset

* Re-added the "yahoo" weather service driver (though it appears to be
non-functional without authentication) -- buyer beware

* Added startup sound "Ready to serve!"

* Other small fix-ups and clean-ups

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* Added OpenWeatherMap.org configurations to control which
forecast timeframe is displayed:

* forecast.today.offset
* forecast.today.cutoff

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* Moved to use OpenWeatherMap.org for weather data

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* Add sample configuration output
* Cleaned up non-Raspberry Pi run/mock mode

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* Made sensors work properly for non-mock GPIO mode