Make logging format configurable (closes #4)

NOTE: the default format for the "test" environment is without
ansi colors, to be easier on remote terminal sessions

config/environments/test.js.example

@@ -4,6 +4,7 @@ var config = {
     ,host: '127.0.0.1'
     ,enable_cors: true
     ,cache_enabled: false
+    ,log_format: '[:date] :req[X-Real-IP] :method :req[Host]:url :status :response-time ms -> :res[Content-Type]'
     ,postgres_auth_user: 'test_cartodb_user_<%= user_id %>'
     ,postgres: {
         user: "publicuser",