message: Chopping yield and worker speed modifiers
  Crop Rotation: +50% chopping yield
  Labour Unions: +50% chopping yield, +50% worker speed
diff: <iCost>650</iCost>
  <iAdvancedStartCost>100</iAdvancedStartCost>
  <Era>ERA_MEDIEVAL</Era>
  + <iFeatureProductionModifier>50</iFeatureProductionModifier>
  <iAsset>32</iAsset>
  <bTrade>1</bTrade>
  <bGoodyTech>0</bGoodyTech>
  <iCost>2400</iCost>
  <iAdvancedStartCost>100</iAdvancedStartCost>
  <Era>ERA_INDUSTRIAL</Era>
  + <iFeatureProductionModifier>50</iFeatureProductionModifier>
  + <iWorkerSpeedModifier>50</iWorkerSpeedModifier>
  <iAsset>56</iAsset>
  <bTrade>1</bTrade>
  <bGoodyTech>0</bGoodyTech>
  