[WIP] Jquery plugin

This is a redesigned version of the jquery widget that is has been part of tangelo.  I'm putting up this PR to collect comments on the API.  Only the basics are implemented at the moment, but you can take it for a spin locally.  `npm install && grunt serve`.  Then go to [http://localhost:8082/examples/jquery-plugin/](http://localhost:8082/examples/jquery-plugin/) for an example.  Also try the docs at [http://localhost:8082/apidocs/$.fn.geojsMap.html](http://localhost:8082/apidocs/$.fn.geojsMap.html), but ignore the mess on the right side of the page.
I think `d3.scale.sqrt()` is a slightly better choice here from a visual perception perspective.