Native jquery events

This adds a compatibility layer between GeoJS and jQuery event handling interfaces.  The GeoJS interface now requires namespacing event handlers like jQuery does it.  Otherwise, the GeoJS object `on`, `off`, and `trigger` methods work the same.   With the compatibility layer, you can now attach handlers with jQuery directly, so the following are equivalent:

```javascript
function doSomething(evt, data) {
  ...
}
$(map).on(geo.event.zoom, doSomething);
$(map).trigger(geo.event.zoom, {}, data);
```

```javascript
function doSomething(data) {
  ...
}
map.on(geo.event.zoom, doSomething);
map.trigger(geo.event.zoom, data);
```

Note the difference in call signature.  For compatibility, the GeoJS methods don't use the jQuery event objects, but I'm willing to consider changing this.  I still need to go through the code to make sure that in source handlers are properly namespaced.
No, `_featureLayer` here is a private namespace added as a convenience.  Users should listen to `geo.event.update`.  Actually, now that I read the [jQuery documentation](http://api.jquery.com/on/) again.  I think it would be better to name our events like this:

```javascript
geo.event.update = "geo-event-update"
```
etc.