DateInRegion's .formatter.useSharedFormatters should be publicly accessible

[malcommac]

DateInRegion's .formatter property should be publicly accessible in order to get/set .useSharedFormatters property (by default is set to true).

This allows the user to use a shared - per thread - formatter or create automatically a new one for each instance of DateInRegion.

Usually user don't need to create a new formatter for each date because it's an expensive operation; however we want to make it possible to cover all cases.