New functions, City::expend_resource() (just a single resource), City::get_mineral_amount().
New functions, City::expend_resource() (just a single resource), City::get_mineral_amount().  In City::do_turn(), pay maintenance after all other income/expenses; actually produce minerals; pay wages & corruption.  Actual gold change should equal that reported by the Minister of Finance now!  All resource-related functions treat resources[] and minerals[] as a single pool for gold and stone.  Use these functions more than just referring to the int[]s for this reason.
Use City::get_resource_amount() rather than City::resources[] since it may pool minerals[] (for gold and stone).