[IMP] observer: add observer to exported objects

src/index.ts

@@ -1,5 +1,6 @@
 export { Component } from "./component";
 export { EventBus } from "./event_bus";
+export { Observer } from "./observer";
 export { QWeb } from "./qweb";
 export { connect, Store } from "./store";
 import * as _utils from "./utils";