Fix bug where power producing facilities would have double output if built first.
keep population and food as integers
test that facility food production increases food levels
increase population over time if not limited by food or land area
make sure pollution is an integer; test limiting of population by land area
Code tidyup, delete unit test I'm not going to implement
integrate with terrain properly, and mock it out in tests
prevent pollution from becoming negative
fix facilityList.update to take the params given by gameStateUpdater
Merge pull request #18 from jmulholland/gameStateUpdater

Implement game state updater (aka world module), with integer numbers and stuff