Move more code into separate classes

It might make logical sense.  Honestly, I'm just tired of the code for
World being so long.

aoe/production.py

@@ -1,12 +1,19 @@
 from collections import defaultdict
 
 from aoe.types import *
+from aoe.exceptions import *
 
 
 
 class Production():
 
 
+    def check_production(self, world, thing):
+        building = self.building[thing]
+        if world.production_available[building] < 1:
+            raise ProductionBuildingNotAvailableException
+
+
     # assumes for now each unit can be built in only one type of building
     def __init__(self):
         self.building = defaultdict(None, {