Save v10->v12: full weather history, fully jsonized .sav.

* future_weather<weather_segment> replaced with map<turn, weather_segment> weather_log, which retains past information as well as pending weather.
* weather data moved out of save/name.sav and into save/name.weather
* memorial log moved out of save/name.sav and into save/name.log
* save/name.sav fully jsonized.
* debug: change weather has a 'view weather log' entry.

With past weather data retention, it will be possible to accurately calculate food decay, bucket filling, solar charging, etc. food decay based on temperature history will be PR'ed soon.