City now stores a pointer to a Game object.  Can be used for fetching the current date, etc.
New function Game::get_date() returns the date.
Set the player's city up with a pointer to our Game.
New function, Player_city::get_population_cap(), tells us the citizen limit for a given Citizen_type (based on Player_city::get_required_ratio().  New enum, struct, and Player_city function allow us to add messages to the city, alerting the player to various events.
New function resource_color() gives a color for a resource.  New function resource_is_meta() tells us if a resource is virtual (like farming or mining).
New function digits_in() returns the number of digits in an int (57 => 2, 1084 => 4, 0 => 1, -34 => 3 (because of the - character)).
in World_map::draw(), debugmsg() if the tile data for the tile we're attempting to draw is NULL.
Use text_data from interface.cuss to print our city's messages, resources and minerals, or citizen information.