redirect / to angular

and also reorganize the middleware/app so that you can easily override `/`.

/cc @stephenplusplus 
This code works for me. I re-ordered/spaced some things that might make it more clear what's going on.

```js
var app = express();

app.get('/', function(req, res) {
  res.redirect('/examples/angularjs');
});

app.get('/_ah/health', function(req, res) {
  res.status(200)
    .set('Content-Type', 'text/plain')
    .send('ok');
});

app.use(todomvc);
app.use('/api', api);

module.exports.api = api;
module.exports.app = app;
```