The main method instantiates an Annex object to provide the City context
before adding 3 Runnable StudentDriver objects (Curly, Larry & Moe) who
display their driving skills as they navigate the Annex.
In order to ensure the liters of fuel are depicted as Things with a dark
gray CircleIcon of size 0.05 it is necessary to override Thing's
makeThing(int n, int total) method.