Add .all() method to get all occurrences of matching dates within a rang...

...e.

This feature allows you to specify a start date, end date and rules, then get all
dates that match falling within that range. Accepts format as it's only parameter.

```js
var recurrence = moment().recur("01/01/2014", "01/07/2014").every(2).days();

// Outputs: ["01/01/2014", "01/03/2014", "01/05/2014", "01/07/2014"]
allDates = recurrence.all("L");
```