Move more code into gather file

aoe/costs.py

@@ -5,6 +5,10 @@ from aoe.types import *
 class Costs():
 
 
+    def compute_cost(self, purchase):
+        return self.costs[purchase]
+
+
     def __init__(self):
         self.costs = {
                       Ages.DARK: (0, 0, 0, 0),