Update path while modifying choroplethChart projection

Hi !
Use case: container of a geoChoroplethChart gets resized. You can just update the geoPath projection to fit the new size, without having to re-render everything. Something like:
```js
var s = container.getSize()
myDcGeoChoroplethChart
       .height(s.height)
       .width(s.width)
       .projection(d3.geo.mercator().translate([s.height/2,s.width/2])); // and the dc takes care of updating the geo path.   
```
Cheers
C.