Use DateTime::Format::XSD to parse $page{date}

[onur]

Dapper is only allowing (\d\d\d\d)-(\d\d)-(\d\d) (\d\d)\:(\d\d)\:(\d\d) formatted dates in date field. I am used to use "YYYY-MM-DD" (ISO) formatted dates in my posts. This patch is using DateTime::Format::XSD to parse date field.

dapper has DateTime::Format::XSD in dependencies. One of filter function is using this module to parse ISO 8601 style date/time format. No external dependency required.