Changes in Build 20181002 cffda6:
- Added new map types: Continents, Islands, Lakes
- Added new map configuration options: water level, climate
- Unit's now can not be upgraded without the required resources (e.g. warrior -> swordsman needs iron)
- Cities attack back at flying units
- Cities' health can't go below zero so that healing is not delayed
- The focus stays on nuclear units after dropping the bomb
- Improved tooltip messages
- Fixed setting LD_LIBRARY_PATH in linux builds which could prevent starting in some cases
- Other minor features and fixes