aileninvasion

1. catch and extract cli --n=6 variables
2. catch and extract file cli --input=cities.txt
3. create a data structure for the map of cities
4. assign aliens to random start points: city.setRandomStartLocation()
5. create a loop function for updating the state: alien.wander(), for(alien a : aliens)
6. create move(), city.getAilenCount(), city.destroyed(), game.isValid()
7. print out world.dump()
8. add comments about assumptions
9. add test case
10. update readme