Returns a new formatter that will use the specified chronology in preference to that of the printed object, or ISO on a parse.
When printing, this chronolgy will be used in preference to the chronology from the datetime that would otherwise be used.
When parsing, this chronology will be set on the parsed datetime.
A null chronology means no-override. If both an override chronology and an override zone are set, the override zone will take precedence over the zone in the chronology.
@param chrono the chronology to use as an override
@return the new formatter