Refacter City::get_crops_grown() and City::get_minerals_mined().  Start a smarter/more complete method of actually generating mined minerals.
In City::do_turn(), remove the current method of gaining minerals (by checking City::get_minerals_mined()) and instead do mines individually, and subtract all minerals produced from the Map_tile they're coming from.  If the Map_tile runs out of the given mineral, it's removed from the Map_tile and from the mine itself (and we fire any workers that were mining it).
Minor refactor.
Include mines and sawmills in Interface::display_area_stats().
Constructor for Terrain_datum.  Terrain_datum tracks a min and max amount of wood; Map_tile tracks how much wood it has.  New function Map_tile::get_terrain_datum().
Set up wood content of tiles in City_map::generate().  New function Map_tile::get_terrain_datum(); use this in City_map::get_terrain_datum().
Wood data.
New function mineral_amount_ranking(); returns a description of how much of the given mineral there is (e.g. "lots of ").