Support for custom renderers

Because `Resolver.render` has an hard dependency on `React.render` it cannot be used with (for example) [`react-titanium`](https://github.com/yuchi/react-titanium) or [`react-blessed`](https://github.com/Yomguithereal/react-blessed).

An initial thought is to transform

``` js
class Resolver {
static render(element, node, instance = new Resolver()) {
React.render((

{element}

), node);

return instance;
}
}
```

to

``` js
class Resolver {
static wrap(element, instance = new Resolver()) {
return (

{element}

);
}
static render(element, node, instance = new Resolver()) {
React.render(Resolver.wrap(element, instance), node);

return instance;
}
}
```

so that I can use it with my renderer, such as

``` js
import { render } from 'react-titanium';
import { wrap } from 'react-resolver';

class App extends Component { /*...*/ }

render(wrap());
```