Openlayers 3 support

Adds support for Openlayers 3. Similar to support for OL2 added in #11 the new API requires the creation of a NodeOverlay which manages an internal OL3 Overlay object. 

Based on and requires #11

Sample usage:

```javascript
// Create the OpenLayers map, add to DOM
var map = new ol.Map({
  layers: [
    new ol.layer.Tile({
      source: new ol.source.Stamen({ layer: 'watercolor' })
    })
  ],
  target: 'map',
  view: new ol.View({
    center: ol.proj.transform([23, 2], 'EPSG:4326', 'EPSG:3857'),
    zoom: 3
  })
});

// Create a content position layer
var locations = new aperture.geo.ol.NodeOverlay();
map.addOverlay(locations.olOverlay);

locations.map('latitude').from('lat');
locations.map('longitude').from('long');
// etc...
```