WorldProperty: year-length n
This property is the number of turns in an annual cycle.
If less than 2, then no seasonal effects will be calculated.
Defaults to 0.
WorldProperty: day-length n
This property is the number of turns in a single day.
If less than 2, then day and night will not be calculated.
Defaults to 0.
Note that year-length and day-length are
completely independent of each other, and it is possible
to have days that are longer than years.
AreaProperty: initial-year-part n
This property is the season of the first turn in the game.
Defaults to 0.
AreaProperty: initial-day-part n
This property is the hour of the first turn in the game.
Defaults to 0.
[need amount of daylight, twilight, etc]
GlobalVariable: season-names xxx
This global is a list of which turns in a year should be called
which seasons. It has the form (... (n1 n2 name) ...).
Defaults to ().