Ensure map dimensions for nonwrapping maps are always even. This may have been causing crashes.
New Temperature option: Eocene, which has only jungle, grassland, and desert.
Arrakis Rainfall option now results in a map with only desert and snow terrain.
Fix a bug where tiles near jungle would be plains unintentionally.
River algorithm faster because it spends less time on tiny islands.
Adjust internal climate graph so that tundra is not slightly dependent on rainfall, tundra forest is less likely the colder it is, and allows Eocene and Arrakis options.