Add "set" Method to "Router"

Hey guys,
I think it would be nice to be able to set options to single Routes. For example one can set a default layout for the handlebars rendering engine with

``` javascript
app.set('view options', { layout: 'main' });
```

or with

``` javascript
app.engine(".hbs", handlebars({
defaultLayout: "main",
}));
```

When using a `express.Router()` for example with `app.use("/admin", adminRouter)` it would be nice to be able to use something like

``` javascript
adminRouter.set('view options', { layout: 'adminMain' });
```

to prevent using

``` javascript
res.render('home', {layout: "adminMain"});
```

for every call to `res.render`

Thanks

-André-