Customizing the format can only be done via getDateFormat

Because of how the dates work now with Carbon they are always converted to a `DateTime` instance in the `fromDateTime` method. Thus, overriding `freshTimestamp` serves no purpose. To customize the date format one must override the `getDateFormat` method.
Merge pull request #387 from jasonlewis/patch-1

Customizing the format can only be done via getDateFormat