[RFR] Allows to add quick filters

![capture d ecran 2014-09-24 a 14 42 32](https://cloud.githubusercontent.com/assets/2076632/4388330/d4dc9a32-43e9-11e4-8aac-1affe22d4042.png)


Usage:
```js
Entity('comments')
.filterParams(function(params) {
    // Allows to return custom specific search params
    return params;
})
.addQuickFilter('Today', function() {
     var now = new Date(),
           year = now.getFullYear(),
           month = now.getMonth() + 1,
           day = now.getDate();

     month = month < 10 ? '0' + month : month;
     day = day < 10 ? '0' + day : day;

     return {
         created_at: [year, month, day].join('-')
     }
 })
```