Add contrib.js

Requiring contrib (in Browserify, webpack, etc) is currently really ugly:

```js
var CollectionView = require('backbone.giraffe/dist/backbone.giraffe.contrib').CollectionView;
```

This makes it prettier :)

```js
var CollectionView = require('backbone.giraffe/contrib').CollectionView;
```
Merge pull request #29 from bobthecow/patch-2

Add contrib.js