code splitting example with webpack 2

[kimown]

Hi, webpack has released 2.2.0, so we can use import to load module dynamically, so I think an official example about react-router and webpack 2 is very necessary.

[justinmasse]

That would be fantastic, been trying to figure out this problem today myself.

[timdorr]

I added Promise support to the async functions in #3719. There are some examples in the tests: https://github.com/ReactTraining/react-router/pull/3719/files#diff-7f51f7b8bcc1ab598f60a81f4bc21724

This is probably better represented as a PR. If you want to put something together, we can definitely work on getting it added in.

[marcofugaro]

So will this work?

<Route path='/page' render={() => import('./components/page')} />

Will webpack effectively split my code by creating a "page.js" file and requesting it only when I navigate to the url /page?