Make startDate option function-compatible

[alexdpunkt]

It would be really helpful if startDate could be a function, in addition to a string.

$(selector).dateRangePicker({

    // Current possibility: string 
    startDate: '04.09.2014',

    // possibility 2: function
    startDate: function() {
        return $('.start-date').val();
    }
});

In my case I need the second datepicker (two separate datepicker setup) to have the startDate of the first date field.

this startDate function should be executed everytime before the datepicker is opened, and set the startDate of the datepicker to the returned date.

[longbill]

good idea, it will support this soon