The previous implementation was ambiguous.

We now set a hit attribute on the click position object.

```javascript
  graph.observe(container, 'flotr:click', function (position) {
          position.hit; // hit information when there is a hit.
            });
```

Fix for #184.  Relates to #129.
Merge branch 'master' of github.com:HumbleSoftware/Flotr2