Format milliseconds id date filter

In some cases there is the need to see not only seconds, but also milliseconds in a formatted date.

I suggest to add to the date filter three milliseconds format:

* `fff`: Millisecond in second, padded (000-999)
* `ff`: Millisecond in second, padded (00-999)
* `f`: Millisecond in second (0-999)

For example:

```
{{1359689000181 | 'MM/dd/yy HH:mm:ss.fff Z'}} => 02/01/13 09:23:20.181 -0600
```