When reading spreadsheets, Spout should be able to return formatted dates, as shown when opened with Excel for instance.
It currently only returns DateTime/DateInterval objects, making it impossible to read + write, as the Writer does not accept objects.
The value passed into the format() function is coming from an XML file and has never been coerced.
Therefore, when checking is_int($value), the check always returns false - because it's a string.
Changing the check fixes the issue and Spout now correctly parses large numbers.
