[WIP] New weather generator.
Provides the essentials for a new weather generator that would give continuous, static pseudo-random procedural weather from a seed. First commit adds the main class that calculates the variables required (temperature, humidity, pressure) and a test function that outputs a csv file for plotting.
It is not yet plugged into the game, but the groundwork is there to replace the update_weather() function in game.cpp.
This is as of now not concerned with the gameplay aspects of weather or adding new weather types. Yet.