+--- Set balance ---
+c SET <user> <balance> <reason>\n
+s 200 Add OK\n or 402 No balance\n or 403 Not Coke\n or 404 Bad User\n
+--- Refund a drink ---
+c REFUND <user> <item>[ <price>]\n
+s 200 Add OK\n or 403 Not Coke\n or 404 Bad User\n 406 Bad Item\n