refactored to a newable object, and updated the examples

Examples are updated. Basic usage is now:
```
 var cedar = new Cedar();
 cedar.show({
     elementId: "#chart",
     spec: "data/charts/simple-bar-chart.json"
   });
```

The intent is that now we have a newable object that can hold state, we can change the api more easily, but did not want to expand this scope to include those changed