Added watch to allow optimistion

expcore/store_test.lua

@@ -0,0 +1,10 @@
+local Store = require 'expcore.store'
+
+Store.register('force.mining_speed','force',function(force)
+    return force.manual_mining_speed_modifier
+end,function(force,value)
+    force.manual_mining_speed_modifier = value
+    game.print(force.name..' how has '..value..' mining speed')
+end)
+
+Store.watch('force.mining_speed','player')