Added credit tracking and stats

Added credit_conversions table so conversions can change over time
Added default credit conversion fixture
Added User#transaction_logs
Added User#total_credits (earned minus spent)
Added User#total_credits_spent (through transaction_logs)
Added User#total_earned_credits (complicated query which finds the conversion rate for a log depending on its created_at date)

db/migrate/20130629152047_create_credit_conversions.rb

@@ -0,0 +1,8 @@
+class CreateCreditConversions < ActiveRecord::Migration
+  def change
+    create_table(:credit_conversions) do |t|
+      t.integer  :conversion, :default => 1
+      t.timestamps
+    end
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20130614003934) do
+ActiveRecord::Schema.define(:version => 20130629152047) do
 
   create_table "bike_actions", :force => true do |t|
     t.string   "action",     :limit => 128, :null => false
@@ -65,6 +65,12 @@ ActiveRecord::Schema.define(:version => 20130614003934) do
 
   add_index "bikes", ["shop_id"], :name => "index_bikes_on_shop_id", :unique => true
 
+  create_table "credit_conversions", :force => true do |t|
+    t.integer  "conversion", :default => 1
+    t.datetime "created_at",                :null => false
+    t.datetime "updated_at",                :null => false
+  end
+
   create_table "customers", :force => true do |t|
     t.string "first_name",  :null => false
     t.string "last_name",   :null => false
@@ -155,9 +161,9 @@ ActiveRecord::Schema.define(:version => 20130614003934) do
   end
 
   create_table "user_role_joins", :force => true do |t|
-    t.integer  "role_id",    :limit => 255
-    t.datetime "created_at",                :null => false
-    t.datetime "updated_at",                :null => false
+    t.integer  "role_id"
+    t.datetime "created_at", :null => false
+    t.datetime "updated_at", :null => false
     t.datetime "ends"
     t.integer  "user_id"
   end

db/seed/fixtures/credit_conversions.yml

@@ -0,0 +1,3 @@
+conversion:
+  id: 1
+  conversion: 10