New function, Building::amount_built(), tells us how much of a given resource the building builds.  It checks whether the city (passed as a parameter) has the necessary resources/minerals to build that resource, and multiplies by the number of workers and the units per day (or divides by the days per unit).  Since this is largely abstracted, it's really only useful for the Minister of Finance.
New functions: City::has_resource{s}(), City::has_mineral{s}(), City::expend_mineral{s}(), and City::get_resource_production().  City::expend_resource{s}() rewritten to use City::has_resource{s}().  City::get_resource_production() sums the result of Building::amount_built() for all buildings/areas.
Add a line to the Minister of Finance for income from mints.  This is basically City::get_resource_production(RES_GOLD).